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Seed physiology presentation

1. http://www.canstockphoto.com/images-photos/seed-pod.html#start:1725 AGRONOMY 52 SEED PHYSIOLOGY NENITA B. BALDO

2. 2 Reproductive Processes in Plants Physiology of Reproductive Growth Plant growth originates in regions within the bud know as meristems It is in this region where cell division and elongation occur resulting to the formation of tissues that soon develop into specific parts Two types of meristems: Vegetative meristems - give rise to parts such as stem, leaves and roots Reproductive meristems – give rise to floral organs that ultimately produce fruits and seeds A. Floral Induction and initiation Primordia - found within every meristem which resemble knobby outgrowths or ribbed inverted cones. - at first, the configuration is hardly visible to the naked eye, however this could be visible when the bud scales are removed and examined under magnification. - as growth proceed, the configurations enlarge and differentiate into recognizable plant organs

3. 3 Reproductive Processes in Plants Physiology of Reproductive Growth Floral Induction Vegetative growth of plants occurs until they are ready to flower Transition from vegetative to reproductive growth involves morphoanatomical, biochemical, and physiological changes. There is a major switch in the pattern of differentiation at the shoot apical meristem which leads to the development of floral organs Physiological change that permits the development of reproductive primordia. This change is induced by external stimuli. - Water - Photoperiod - Chemicals - Nutritional status - Temperature

4. 4 Reproductive Processes in Plants Physiology of Reproductive Growth Floral initiation – signals the end of leaf reproduction. This is the followed by pollination, fertilization, embryo development and fruit ripening. FLORAL INITIATION - Morphological expression of the induced state . Usually occurs within the meristems of a plant . Types of plants: Annuals x biennials x perennials FLOWERING - PHASE OF THE PLANT LIFE CYCLE THAT PROMOTES FRUIT AND SEED

5. 5 Reproductive Processes in Plants Physiology of Reproductive Growth Flowering occurs at shoot apical meristems. The ability to flower ( i.e the transition from juvenility to maturity) is attained : When a plant reached a certain age or size, independent of the environment ( autonomous induction) or has achieved the state or ripe- to respond ( competence ); the change in the meristem from vegetative to reproductive growth is called evocation; the meristem is said to be competent ; and when induced ( i.e. exposed to correct daylength [photoperiodism] or temperature [vernalization] is required

6. 6 Reproductive Processes in Plants Physiology of Reproductive Growth B. Factors influencing floral induction and initiation 1. Day-length stimuli Photoperiodism – is a response to length of day or photoperiod. however it is really the length of night, or dark period that is critical factor that influences flowering. Type of plants based on their daylength requirements: a. Short-day plant (SDP) - flower when a critical duration of darkness is exceeded. Ex. Chrysanthemum, tobacco, poinsettia, sweet potato, & strawberry, b. Long-day plant (LDP) – flower when the length of the dark period is less than the critical value. Ex. Most cereal grains, timothy, clover, hibiscus and Irish potato c. Day-neutral plant – not affected by photoperiod. Ex. Tomato, field bean, zinnia, dandelion and chickweed. FLORIGEN - flowering hormone /stimulus that is perceived by leaf. It is transported via the phloem and reaches the apex, resulting in floral evocation, flower initiation and flower formation

7. 7 Florigen (or flowering hormone ) is the hypothesized hormone -like molecules responsible for controlling and/or triggering flowering in plants. Florigen is produced in the leaves , and acts in the shoot apical meristem of buds and growing tips. It is known to be graft-transmissible, and even functions between species. However, despite having been sought since the 1930s, the exact nature of florigen is still a mystery . The mechanism may be broken down into three stages: photoperiod-regulated initiation , signal translocation via the phloem, and induction of flowering at the shoot apical meristem .

8. 8 Reproductive Processes in Plants Physiology of Reproductive Growth The transition from vegetative to reproductive growth is controlled by day length in many plant species. Day length is perceived in leaves and induces a systemic signal, called florigen , that moves through the phloem to the shoot apex. At the shoot apical meristem (SAM), florigen causes changes in gene expression that reprogram the SAM to form flowers instead of leaves. Analysis of flowering of Arabidopsis thaliana placed the CONSTANS / FLOWERING LOCUS T ( CO / FT ) module at the core of a pathway that promotes flowering in response to changes in day length .

9. 9 Initiation In Arabidopsis thaliana , the signal is initiated by the production of messenger RNA (mRNA) coding a transcription factor called CONSTANS (CO). CO mRNA is produced approximately 12 hours after dawn, a cycle regulated by the plant's biological clock. This mRNA is then translated into CO protein. However CO protein is stable only in light, so levels stay low throughout short days and are only able to peak at dusk during long days when there is still a little light . CO protein promotes transcription of another gene called Flowering Locus T (FT ). By this mechanism, CO protein may only reach levels capable of promoting FT transcription when exposed to long days. Hence , the transmission of florigen -- and thus, the induction of flowering-- relies on a comparison between the plant's perception of day/night and its own internal biological clock .

10. 10 Translocation The FT protein resulting from the short period of CO transcription factor activity is then transported via the phloem to the shoot apical meristem . Flowering At the shoot apical meristem the FT protein interacts with a transcription factor, FD protein, to activate floral identity genes, thus inducing flowering. Specifically , arrival of FT at the shoot apical meristem and formation of the FT/FD heterodimer is followed by the increased expression of at least one direct target gene, APETALA 1 (AP1 ), along with other targets, such as SOC1 and several SPL genes, which are targeted by a microRNA .

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12. 12 ) Vernalization – is an effect on flowering brought about by the exposure to very low temperature. The dark period is extra important since it can be made ineffective by interruption with a short exposure to light. This process is called a night break. In contrast, interrupting a long day with a brief dark period does not cancel the effect of the long day. Night break treatments are effective in preventing flowering in SDP but promote flowering in LDP. GA is particularly effective in triggering flower formation of many LDP. The night break inhibition of flowering in SDP shows that the light signal causing photoperiodic response is under phytochrome control. A night break is only effective if the dose of supplied light is sufficient to saturate the photoconversion of Pr to Pfr Subsequent exposure to far-red light, which photo converts the pigment back to the inactive Pr form .

13. 13 ) Vernalization – is an effect on flowering brought about by the exposure to very low temperature. Red is the most effective wavelength in night break . A flash of red (or white) light during the dark period induces flowering in LDP (high amount of Pfr needed). The effect, if reversed by a flash of far-red light, indicates the involvement of phytochrome. In SDP, a flash of red light p revents flowering. Role of phytochrome activation of specific genes in the leaf that could regulate floral induction; and or, 2. Modification of membrane properties

14. 14 Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night ( photoperiodism) and to set circadian rhythms. It also regulates other responses including the germination of seeds ( photoblasty ), elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings. It is found in the leaves of most plants. Biochemically, phytochrome is a protein with a bilin chromophore . Phytochrome has been found in most plants including all higher plants; very similar molecules have been found in several bacteria . A fragment of a bacterial phytochrome now has a solved three- dimensional protein structure. Other plant photoreceptors include cryptochromes and phototropins , which are sensitive to light in the blue and ultraviolet regions of the spectrum . http://en.wikipedia.org/wiki/Phytochrome

15. 15 Phytochrome responses:   Important plant responses regulated by the phytochrome system include photoperiodic induction of flowering , chloroplast development (not including chlorophyll synthesis), leaf senescence and leaf abscission . Characteristics of phytochrome-mediated responses: The action spectrum of the light needed for these responses shows a peak in the red at about 660 nm. These responses can be reversed by an application of far-red light ( peak at 730 nm) soon after the red treatment. Sensitive spectrophotometers can measure a decrease in absorbance at 660 nm and in increase in absorbance at 730 nm when sensitive plant tissues are exposed to red (660 nm) light. The change in absorbance is caused by the conversion of a the photoreceptor from one structural form to another.  The red- absorbing form changes to the far-red absorbing form when it absorbs red light (660 nm) and back again when it absorb far-red light ( 730 nm).

16. 16 The phytochrome molecule is the photoreceptor for red light responses.  It exists in two forms, Pr and Pfr : The Pr form: Absorbs at a peak of 660 nm Is the form synthesized in dark-grown seedlings. When Pr absorbs red light, it is converted to the Pfr form. The Pfr form: Absorbs at a peak of 730 nm The Pfr form is the active form that initiates biological responses When Pfr absorbs far red light, it is converted to the Pr form Pfr can also spontaneously revert to the Pr form in the dark over time = dark reversion; Pfr is also susceptible to proteinases. Pfr absorbs some red light, so in red light, there is a balance of 85% Pfr and 15% Pr Pr absorbs very little far red light, so in far red light, there is a balance of 97% Pr to 3% Pfr

17. 17 The Phytochrome System and Its Control Possibilities (according to P.H.QUAIL, 1984)

18. 18 Phytochrome and the control of flowering. Flowering Cues: Plants with have to coordinate the production of flowers to coincide the best reproductive opportunities. There are many environmental cues that affect flowering however the photoperiod is the most reliable indicator on 'time' of year. The photoperiod. Its the period of day light in relation to dark (night). In northern and southern regions of the world, this photoperiod is a reliable indication of the time of year and therefore one of the most reliable indicators of the seasonal changes.

19. 19 Phytochrome and the control of flowering. Flowering Cues: Short and Long day Plants: Short day plants (SDP) typically flower in the spring or autumn when the length of day is short. Long day plants (LDP) typically flower during the summer months of longer photoperiod. Critical Night Length: Experiments have shown that the important factor determining flowering is the length of night rather than the length of day. Therefore it may help students to remember SDP have a critical long night. That the length of night has to exceed a particular length before there will be flowering. LDP have a critical short night. That the length of night must be shorter than a critical length before there will be flowering. e.g . Cocklebur is an SDP with a critical night length of 9 hours, when flowering will occur. A shorter night does not produce flowering. (It is worth noting that this is not the only combination of environmental triggers that bring about flowering)   http ://click4biology.info/c4b/9/plant9.3.htm

20. 20 Phytochrome System: The receptor of photoperiod is located within the leaf. The cellular location of the receptor is unclear. The chemical nature of the receptor is the molecule PHYTOCHROME. Phytochrome can be converted from one form to another by different types of light. http://click4biology.info/c4b/9/plant9.3.htm

21. 21 Flowering in SDP : Short day plants flower when the night period is long. In day light or red light, Phytochrome Red ( Pr ) is converted to Phytochrome Far Red ( Pfr ). The conversion actually only requires a brief exposure to white or red light. In the dark, Pfr is slowly converted back to Pr. A long night means that there is a long time for the conversion. Under short day conditions (long night) at the end of the night period the concentration of Pfr is low. In SDP, low Pfr concentration is the trigger for flowering. http://click4biology.info/c4b/9/plant9.3.htm

22. 22 Flowering in LDP: Long day plants flower when the night period is short. In day light (white or red) the Pr is converted to Pfr . During periods when the day light period is long but critically the dark period is short, Pfr does not have long to breakdown in the dark. Consequently there remains a higher concentration of Pfr . In LDP, high Pfr concentration is the trigger to flowering . The mechanism of flowering: The search for the substance that causes the development of meristematic tissue into flowers was focused on the identification of ' florigen ', the flowering hormone. Phytochrome Fr ( Pfr ) is the biologically active form of phytochrome but it is florigen that can be translocated . Most research indicates that phytochrome cannot move from the leaf cells to the meristem tissue. http://click4biology.info/c4b/9/plant9.3.htm

23. 23 In 2005 a substance, mRNA (FL mRNA) was finally isolated that was found to be moving from leaf to flower meristem. This mRNA provides a link between the phytochrome system (the receptor), its activation of genes in the leaf (mRNA synthesis) and the differentiation of the meristem into the flower structure. The mechanism of flowering: ( con’t ) http://click4biology.info/c4b/9/plant9.3.htm

24. 24 2. Temperature stimuli Vernalization – process of exposing the plant to low temperature for flower induction to occur. In its narrow sense, vernalization means the promoting of flowering to some winter cereals by cold treatment of the moistened or germinating seeds. In its broader sense, vernalization, means the low temperature induction of flowering in any winter annual, biennial or even perennial species. Example: rye ( Secale cereale )- winter annual both need perennial ryegrass ( Lolium perenne ) prolonged exposure to low temperature before they will produce flowers. Sugar beets and carrots (biennial species) – grow vegetatively in the first year , after which they are vernalized by exposure to winter temperature Chrysanthemum & tomato – floral induction is accomplished by repeated exposure to low night temperatures, separated by periods of high temperature.

25. 25 2. Temperature stimuli Vernalization – is the process whereby (earlier )flowering by giving seeds that have imbibed water or growing plants a cold treatment. Dry seeds do not respond to cold treatment. Ineffective in the absence of oxygen, water and adequate supply of carbohydrates for respiratory process Primarily takes place in the meristematic zones of the shoot apex . Effective temperature for vernalization: just below freezing to about 10 o C, with broad optimum between 1 and 7 o C Effect of cold treatment increases with its duration, until response is saturated Duration varies widely with species and varieties The longer the cold treatment, the more permanent is the effect of vernalization ( excised shoot tips or fragments of embryos [with shoot tip] have been successfully vernalized. VERNALIN – vernalizing stimulus (a hypothetical substance)

26. 26 2. Temperature stimuli Photoperiodism may interact with vernalization Most common combination = cold treatment followed by a requirement of long day. Cold treatment, followed by long days, can promote bolting (rapid elongation of flowering shoot) in some rosette species. 3. Chemical Stimuli Natural and synthetic chemical substances can cause flora induction 1 . Auxinlike compounds ex. Indoleacetic acid (IAA), naphthaleneacetic acid (NAA), 2,4 dichlorophenoxyacetic acid (2,4D), Gibberellic acid (GA) at certain concentration. 2. Other substances includes: cytokinins , ethylene, acetylene, ethylene cholorohydrin and 2,3,5-triodobenzoic acid Maleic hydrazide inhibits flowering

27. 27 4. Nutritional status : important since flowering is dependent on food availability and translocation. Carbon:nitrogen ratio – ex. in holly that bear male and female flower on separate plants. High N to C ratio favors pistillate rather than staminate flowers Tomatoes – carbohydrate deficiencies, causes microspore degeneration, leading to pollen sterility. Floral Initiation –Follows after floral induction (triggered by external stimuli) is the morphological expression of the induced state and usually occurs more or less deeply within the plant meristems. Monocot species or flowering plants in which single embryonic seed leaf appears at germination, floral initiation begins in specialized meristems called dermatogens , also give rise to epidermis Dicot species (pair of embryonic seeds appear during germination), floral initiation occurs in the lateral, terminal, or axillary buds.

28. 28 FLORAL INITIATION During the early development, reproductive meristems are similar vegetative meristems (appear as knobby or ribbed configurations) As the development continue, the configurations develop into a recognizable flower parts.

29. 29 L ocule -refers to a chamber within an ovary (gynoecium or carpel of the flower and fruits. Depending on the number of locules in the ovary, fruits can be classified as uni-locular , bi- locular or multi- locular . The number of locules present in a gynoecium may be equal to or less than the number of carpels. The locules contain the ovules or seeds A bi- locular tomato fruit. A multi- locular tomato fruit. locule funiculus Ovary wall (pericarp) ovule

30. 30 Typical Flower of an Angiosperm (seeds enclosed in an ovary) 1. Sepals – Less conspicuous, collectively called calyx 2. Petals – Most conspicuous part of a flower, collectively called corolla 3. Stamens – male pollen-bearing organ (androecium), consist of an anther and filament 4. Pistils (gynoecium) – female part of the flower and consist of stigma, style, ovary and ovule Amaryllis stigmas and style Centre of a Ranunculus repens (Creeping Buttercup) showing multiple unfused carpels surrounded by longer stamens. Centre of a Tulipa aucheriana ( Tulip ) showing multiple connate carpels (a compound pistil) surrounded by stamens. wikipedia.org/wiki/Gynoecium FLORAL MORPHOLOGY

31. 31 Floral Morphology Parts of a Complete flower

32. 32 Christmas Lily ( Lilium longiflorum ). 1. Stigma, 2. Style, 3. Stamens, 4. Filament, 5. Petal Another example of a complete flower

33. 33 FLORAL MORPHOLOGY Complete flowers = flowers having pistils, stamens, petals, and sepals Incomplete flowers = flowers lack any of the above four parts. Perfect = flowers containing both stamens (male) and pistils (female) Imperfect = unisexual flowers which are either pistillate or staminate Monoecious plants = species that have both male and female flowers on the same plant. Ex. Corn Dioecious plants = unisexual flowers are found on different plants of the same species. Ex. Papaya FLORAL TAXONOMY The arrangement of the floral axis determines the type of inflorescence and is stable characteristics Inflorescence = the arrangement or manner in which flowers develop on a stalk Peduncle = main stalk of the inflorescence Pedicels = lateral stalks supporting the individual flowers

34. 34 FLORAL MORPHOLOGY Ovary -may composed of one or more carpels, (highly modified leaflike structure Simple ovary = consist of only one carpel and one locule or cavity Compound ovary = made up of two or more united carpels and may contain one or more locules, depending on their arrangement. Pericarp = outermost wall of the ovary Placentation = manner in which the seeds are attached to the placenta within the ovary locules Type of Placentation: Parietal – occurs when the seeds are attached to the ovary wall, usually to both sides of the seam where the carpels fuse to form the ovary Axile – occurs in flowers with ovaries divided by partitions, called septa Free central – occurs when no septa are present in the ovary and the seeds are attached along the central axis ( basal and apical placentation is a type of modification)

35. 35 Types of Flowers Determinate Flowers Solitary flowers – The simples expression of determinate inflorescence. Example okra Simple cyme – The simplest branched determinate inflorescence where the lateral flowers develop later than the terminal flower. Ex. Chickweed Compound cyme – A determinate inflorescence where there is secondary branching and each lateral unit becomes a simple cyme. Ex. Tropical ageratum Scorpioid cyme – A determinate inflorescence in which the lateral buds on one side are suppressed during growth, resulting in a curved or coiled arrangement. Ex . Heliotropium curassavicum ) Indeterminate Flowers 1. Raceme The basic type of inflorescence in which pedicels arise laterally on a long central peduncle 2. Spike -

36. 36 FLORAL TAXONOMY Inflorescence may be determinate or indeterminate Determinate Flowers a. Solitary flower = simplest expression of determinate inflorescence. Ex. Okra b. Simple cyme = The simplest branched determinate inflorescence where the lateral flowers develop later than the terminal flower c. Compound cyme = determinate inflorescence where there is secondary branching and each lateral units becomes a simple cyme. d. Scorpioid cyme = determinate inflorescence in which the lateral buds on one side are suppressed during growth, resulting in a curved or coiled arrangement. e. Glumerole = a very compact compound cyme Indeterminate Flowers Raceme – The basic type of inflorescence in which pedicels arise laterally on a long central peduncle. Ex. mungbean b. Panicle – An inflorescence in which the lateral branches arising from the peduncle produce flower-bearing branches instead of single flowers. Ex. Oat, rice, sorghum, corn tassel

37. 37 FLORAL TAXONOMY Indeterminate Flowers c. Spike – An inflorescence in which the flowers arising along the peduncle are essentially sessile, or stalkless , and are attached to the peduncle. Ex. wheat d. Catkin – A modified type of spike with a single unisexual flower arising from the peduncle. Ex. Red alder e. Spadix – A special kind of spike covered by a spathe . Ex. Skunk cabbage, anthurium, gabi Corymb – An inflorescence in which the lower pedicels arising from the peduncle are successively longer than the upper ones giving a round or flat-topped appearance. Ex. Bitter cherry Umbel – An inflorescence similar to a corymb except that the lateral branches arising from the peduncle originate from the same location Compound umbel – similar to umbel except that each pedicel is branched, bearing multibranched individual flowers. Ex. Wild carrots Head – An inflorescence where the peduncle and the pedicels are tightly clustered, surrounded by a group of flowerlike bracts called and involucre. Ex. sunflower

38. 38 TYPES OF INFLORESCENCE Collective cluster of flowers

39. 39 FRUIT DEVELOPMENT To understand seed formation one must have a basic knowledge of fruit development and morphology. Fruit (botanical definition) – is a mature or ripened ovary that usually contains one or more ovules that develop into true seeds. Example of fruits: legume pods, peppers and cereal grains; apples, oranges and peaches Parts of a fruit: 1. pericarp or ovary wall – composed of three different layers a. exocarp – outer layer b. mesocarp – middle layer c. endocarp – inner layer Fruit Types 1. Psuedocarpic fruit - consists of one or more ripened ovaries attached or fused to modified bracts or other nonfloral structures. Ex. Sandbur 2. Multiple fruit – composed of the ovaries of more than one flower. Each units of these fruits maybe berries, drupes,, or nutlet or a berry. Ex. Strawberry, raspberry, huckleberry. 3. S imple fruit – derived from a single pistil

40. 40 TYPES OF FRUITS 1) Drupe /stone fruit : fruit usually with a fleshy mesocarp and a single seed enclosed in a hard stony endocarp or pit (e.g. plum). Notes: 1) walnut mesocarp is hard when ripe; 2) holly drupes have 4 – 6 pyrenes (seeds each in own hard endocarp). Ex. Coconut, Fruit Types © Kwantlen A . Fleshy Fruits - have fleshy or leathery pericarp

41. 41 TYPES OF FRUITS 2) True berry: fleshy fruit ( mesocarp + endocarp) with thin skin ( exocarp ) and many seeds (e.g. grape) Fruit Types©Kwantlen .

42. 42 TYPES OF FRUITS 3) Berry (tomato): pericarp ( exocarp , mesocarp , endocarp), seed, locule , placenta

43. 43 TYPES OF FRUITS 4) Pepo : a berry with a relatively thick rind ( Cucurbitaceae , e.g. squash) which is derived from the receptacle (accessory tissue).

44. TYPES OF FRUITS 5) Hesperidium: a berry with leathery outer skin containing oils; carpels evident in cross section ( Rutaceae e.g. lime)

45. TYPES OF FRUITS 6) Pome: fruit with leathery or papery endocarps surrounded by fleshy accessory tissue derived from the floral tube 7) Pome (apple): pedicel, calyx, accessory tissue (derived from the floral tube), pericarp ( exocarp , mesocarp , endocarp), seed, locule

46. TYPES OF FRUITS 8) Rose hip: similar to pome except it contains many achenes (an aggregate fruit type)

47. TYPES OF FRUITS Aggregate fruit : f ruit divided from a single flower having several to many pistils (e.g. magnolia is an aggregate of one-seeded follicles; tulip tree of samaras) Fruit Types©

48. TYPES OF FRUITS Multiple fruit:derived from several to many separate flowers in an inflorescence, the fruit uniting to form a single fruit at maturity (e.g. fig) Fruit Types©Kwantlen

49. TYPES OF FRUITS 11) Samara (key): indehiscent dry fruit with one or more wing (e.g. maple, ash, tree of heaven ) Fruit Types©Kwantlen.ca/Horticulture

50. TYPES OF FRUITS 12 ) Nut: indehiscent dry fruit with a hard shell surrounding the seed (compound pistil but only one seed usually develops after the rest abort, e.g. hazelnut). Note: beech (top right) has 3-angled nuts from compound ovary enclosed in prickly bracts that split open like a capsule.

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