PHYSIOLOGY AND BIOCHEMISTRY OF SEED GERMINATION.pptx

PHYSIOLOGY AND BIOCHEMISTRY OF SEED GERMINATION

1. PHYSIOLOGY AND BIOCHEMISTRY OF SEED GERMINATION SEED : seed is a ripe , fertilized ovule GERMINATION : The process that begins with the water uptake by the dry seed and ends with the emergence of the embryonic axis usually the radicle from its surrounding tissue Physiology of Seed Germination Annual Review of Plant Physiology Vol . 7:299-324 (Volume publication date June 1956)

2.   Seed germination is defined as the sum of events that begin with hydration of the seed and culminate in emergence of the embryonic axis (usually the radicle) from the seed coat. Plant Growth and Development: Hormones and Environment, 2002 Seed Germination

3. SEED GERMINATION Activation of embryo Seed germination is a mechanism, in which morphological and physiological alterations result in activation of embryo elongation Before germination, seeds absorb water, resulting in the expansion and elongation of seed embryo Emergence of radicle When the radicle has grown out of the covering seed layers, the process of seed germination is completed ( Hermann el al., 2007 )

4. REQUIREMENTS FOR GERMINATION Water Gasses Temperature light Nitrates

5. GASSES

6. TEMPERATURE

7. Physiology of Seed Germination Seed imbibition leads to ROS and NO accumalation .ROS regulate ABA catabolism through NO & GA biosynthesis A high concentration of ABA also inhibits GA biosynthesi s But a balance of these two hormones jointly controls seed dormancy and germination

8. 1 . Water uptake Seed germination  starts with the imbibition of water by dry seed coat. Various hydrophilic groups such as —NH 2 , — OH, — COOH etc., of proteins, polymeric carbohydrates etc ., found in the seed coat attract dipolar water molecules and form hydrated shells around them resulting in the swelling of these substances. Due to imbibition of water the seed coat becomes more permeable to O2 and water and less resistant to outward growth of embryo. After imbibition, the inner contents of the seed increase in volume, thereby exerting pressure on the seed coat leading to rupture of the seed coat. The plumule and radical emerge thereafter.

9. water uptake by dry seeds exhibits three phases ( Bewley , 1997 ). Bewley , J.D., 1997. Seed germination and dormancy. Plant Cell 9 (7), 1055 1066.

10. 2 . Respiration After initiation of germination process, enormous energy is required for various biochemical changes which are met through rapid increase in respiration rate. Sucrose is probably the respiratory substrate at this stage which is provided by endosperm. In oilseeds and pulses, the lipids and proteins respectively are converted into sucrose by suitable biochemical reactions.

11. Respiration The uptake is accompanied by rapid increase in respiration rate of embryo. Initially there may be anaerobic respiration but it is soon replaced by aerobic one due to availability of O 2 . As compared to dry seeds, the uptake of O 2  in germination seeds may rise within very short period after germination when water content has reached about 40%. Sucrose is probably the respiratory substrate at this stage which is provided by endosperm.

12. PHASE –I Imbibition is a physical process related to matric forces that occur in dry seeds with water permeable seeds whether they are alive or dead ,dormant or non dormant initially ,water uptake is very rapid over the first 10 to 30 minutes. This is followed by slower wetting stage for up to an hour for small seeds or several hours 5 – 10 hrs for large seeds water uptake eventually ends as the seed enters lag phase of germination The process of germination starts with seed imbibition/uptake of water by the dry seed and terminates with radicle penetration through the seed covering layers ( Bewley , 1997; Weitbrecht et al., 2011 ). Bewley , J.D., 1997. Seed germination and dormancy. Plant Cell 9 (7), 1055 1066. Weitbrecht , K., Mu¨ller , K., Leubner -Metzger, G., 2011. First off the mark: early seed germi - nation. J. Exp. Bot. 62 (10), 3289 — 3309.

13. Phase I: This is characterized by a sharp rise in respiration for about 10 hours and is due to the activation and hydration of mitochondrial enzymes belonging to the cycle and electron transport chain. Researches on Plant Respiration. I.— The Course of Respiration of Lathyrus odoratus during Germination of the Seed and the Early Development of the Seedling . By Walter Stiles, Sc.D., F.R.S., and William Leach, M.Sc., Ph.D. (Received June 6, 1932.)

14. Phase II This involves a lag in respiration between 10 and 25 hours after the start of imbibition. Hydration of the cotyledons is now completed and all pre-existing enzymes activated. It is interesting to note that there is rapid oxygen uptake into seeds with intact testas during phase I (early imbibition), whereas the same testa impedes oxygen uptake in phase II. Between phase II and phase III, the radicle penetrates the testa . eetambar Dahal , Nahm -Su Kim1 and Kent J. Bradford2 Respiration and germination rates of tomato seeds at suboptimal temperatures and reduced water potentials Journal of Experimental Botany, Vol. 47, No. 300, pp. 941-947, July 199

15. Phase III A second respiratory surge characterizes this phase which is thought to be due to increased oxygen supply through pierced testa . Another reason for respiratory increase should be the newly synthesized mitochondria and respiratory enzymes in the dividing cells of the growing axis.

16. Phase IV: This is characterized by a marked fall in respiration that coincides with the disintegration of the cotyledons following exhaustion of the stored food. It has been shown that in the early stages of germination, respiration is cyanide-resistant and the alternative oxidase instead of cytochrome oxidase plays a role in germination.

17. 3. Mobilization of reserve materials As germination progresses, there is mobilization of reserve materials to provide . 1. Building blocks for the development of embryo 2. Energy for the biosynthetic process 3. Nucleic acids for protein synthesis and embryonic development

18. 1 . Nucleic acids D uring imbibition, there is a rapid decrease of DNA and RNA contents in the endosperm with a simultaneous increase in the embryonic axis. High concentration of RNA in the embryonic axis precedes cell division. Due to more cell division DNA content is increased. Changes in Nucleic Acid Fractions of Seed Components of Red Pine ( Pinus resinosa Ait .) During Germination' S . Sasaki and G. N. Brown School of Forestry, University of Missouri, Columbia, Missouri 65201 Received July 9, 1969. Abstract. Changes in nucleic acid fractions of Pinus resinosa during seed g

19. 2 . Carbohydrates In the endosperm. During germination starch is hydrolysed first into maltose I n the presence of α-amylase and β-amylase and then the maltose is converted Into glucose by maltase. The glucose is absorbed by the scutellum , converted Into soluble sucrose and transported to growing embryonic axis .

20. 2 . Carbohydrates

21. 3 . Lipids Many plants like castor bean, peanut, etc , store large amount of lipids or fats as reserve food in their seeds. During germination, the fats are hydrolyzed into fatty acids and glycerol by lipase enzyme. Fatty acids are further converted into acetyl – COA by the process of ß - oxidation. The acetyl COA is further converted into sucrose via glyoxylate cycle and is transported to the growing embryonic axis. FATS FATTY ACIDS AND GLYCEROL ACETYL –COA SUCROSE

22. 4 . Proteins Some plants store proteins as reserve food in their seeds. Proteins are hydrolyzed into amino acids by peptidase enzyme. The amino acids may either provide energy by oxidation after deamination (removal of amino group) or may be utilized in the synthesis of new proteins. Some plants store proteins as reserve food in their seeds in the form of aleurone grains. Mobilization of these proteins involves their hydrolytic cleavage into amino acids by peptidases .The amino acids may either provide energy by oxidation after deamination or may be utilized in the synthesis of new proteins .

23. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of present proteins in the  L. campestris  germinated seed. S = standards ( kDa ). C . Jiménez Martínez , 1  A. Cardador Martínez, 2  A. L. Martinez Ayala, 3  M. Muzquiz, 4  M. Martin Pedrosa, 4  and  G. Dávila -Ortiz , Changes in Protein, Nonnutritional Factors, and Antioxidant Capacity during Germination of  L. campestris   Seeds ,International J ounal of Agronomy : Volume 2012  ; Article ID 387407  L . campestris seeds subjected to different germination times. As it is observed the seed without any germination time showed greater amount of protein bands located between 20 and 75  kDa . As the germination time advances, the proteins located in the range of 28–49 and 49–75  kDa almost disappeared after nine germination days of Lupinus seed, and there was an increase in bands about 27  kDa . These results confirm previous findings about storage proteins, which are hydrolysed and mobilised after germination [21, 22]. This behavior lets us to suggest that the principal storage protein molecules, the globulins 7 s, and 11 s constituted by three and six subunits, respectively, were hydrolyzed in lower molecular weight compounds which has a best digestibility and consequently a better biological value .

24. PROTEIN

25. 5.Inorganic nutrients A number of inorganic nutrients such as phosphate, calcium, magnesium and potassium are also stored in seeds in the form of phytin . These stored nutrients are liberated during germination due to the activity of various phosphatases including phytase . EXP : After 96 h germination, the dry weight of fenugreek seeds decreased while total ash content increased. Phytase and phosphatase activity of the ungerminated and germinated seeds have been assayed. It is observed that during germination the phytic acid values diminish and the water soluble inorganic phosphorus values increase . Changes in calcium, magnesium, iron, manganese, copper and zinc are found to be dependent on the loss of dry weight which occurs during processing of fenugreek seeds . Ahmed RafikEl-MahdyLaila A.El-Sebaiy ; Changes in phytate and minerals during germination and cooking of fenugreek seeds; Elrsevier ;Food Chemistry Volume 9, Issue 3 , October 1982, Pages 149-158

26. Emergence of seedling out of the seed coat: result in splitting of seed coat and emergence of the growing seedling. First, the radicle comes out and grows downward, then plumule comes out and grows upward. Due to continued growth of this seedling, the latter comes out of the soil, exposed to light and develops its own photosynthetic apparatus. The splitting of seed coat may take place either: ( i) By imbibitional pressure or (ii ) By internal pressure created by the growing primary root or (iii) By hydrolytic enzymes which act on cell wall contents of seed coat and digest it e.g., cellulase , pectinase etc. Sometimes the seed coat may be extensively rotted by the activity of micro-organisms in the soil. plant growth and development chapter 15 - NCERT

27. THANK YOU Mrs D.Saritha Ph.D Scholor Ist yr