Plant physio

• Cytokinins


  A class of plant hormones, synthesized predominantly in the roots of plants, with significant activity occurring in the root tips and vascular tissues
• Synthesis of cytokinins

  Multistep biosynthesis pathway primarily in root tissues, involving conversion of adenine derivatives like ATP into active cytokinin forms like isopentenyladenine and trans-zeatin
• Ethylene


  A plant hormone/growth regulator, synthesized in ripening fruits and tissues undergoing senescence
• Biosynthesis of ethylene


  From S-adenosyl-l-methionine (SAM) via 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase
• Abscisic acid (ABA)


  A sesquiterpenoid plant hormone
• Molecular structure of ABA

  • 15-carbon backbone derived from carotenoids, contains carboxylic acid group and cyclohexene ring
• Biosynthesis of ABA


  Initiated in chloroplasts, completed in cytosol, involving conversion of glyceraldehyde-3-phosphate and pyruvate to isopentenyl pyrophosphate and then to xanthoxin, which is exported to cytosol and converted to ABA
• Methods of ABA detection

  • Chromatography techniques like HPLC and GC-MS
  • Immunoassay methods like ELISA
  • Biosensor technologies utilizing ABA receptors or responsive elements
• Catabolism of ABA


  Oxidation to phaseic acid, further metabolization to dihydrophaseic acid and conjugation with sugars
• Translocation of ABA


  Synthesized primarily in leaves, fruits, and root caps, transported via xylem and phloem to other plant parts, especially under water stress conditions
• Types of plants based on photoperiod

  • Short-day plants
  • Long-day plants
  • Day-neutral plants
• Perception of photoperiodic stimulus

  Leaves perceive the photoperiodic stimulus, produce a floral hormone that is translocated to the apical tip to initiate flower development
• Critical photoperiod


  Minimum duration of light required to induce flowering, perceived by photoreceptors like phytochromes and cryptochromes
• Florigens


  Proteins capable of inducing flowering time in angiosperms, produced in leaves and act in shoot apical meristem
• Gibberellins


  Plant hormones that regulate processes like stem elongation, germination, dormancy, flowering, flower development and leaf and fruit senescence
• Critical photoperiod


  The minimum duration of light required to induce flowering
• Photoreceptors in plants

  • Phytochromes and cryptochromes perceive the light stimulus and produce signals that regulate flowering based on the critical length of photoperiod
• Biloxi soybean variety


  • Short-day plant that flowers when the day length is shorter
• Maryland Mammoth tobacco


  • Long-day plant that flowers during shorter days
• Florigens (or flowering hormone)


  Proteins capable of inducing flowering time in angiosperms
• Prototypical florigen


  Encoded by the FT gene and its orthologs in Arabidopsis and other plants
• Florigens


  • Produced in the leaves, and act in the shoot apical meristem of buds and growing tips
• Gibberellins (GAs)


  Plant hormones that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence
• Phytochromes


  A class of photoreceptor proteins found in plants, bacteria and fungi that respond to light in the red and far-red regions of the visible spectrum
• Phytochromes


  • Can be classed as either Type I, which are activated by far-red light, or Type II that are activated by red light
• Vernalization


  A process in which plants require exposure to prolonged cold temperatures to initiate or accelerate flowering
• Vernalization is particularly crucial for biennial and winter annual plants to ensure they flower in the appropriate season
• Vernalization


  • Helps plants synchronize their reproductive cycles with favorable environmental conditions, typically occurring in spring
  • Involves molecular changes in the plant's cells, including alterations in gene expression related to flowering
• Devernalization


  The reversal or inhibition of vernalization due to exposure to warmer temperatures after the cold period
• In most species the effect of a vernalizing cold treatment can be partially or totally eliminated by several days of heat treatment, typically 30–40 °C (devernalization)
• Devernalization


  • Can lead to delayed or inhibited flowering, affecting the plant's reproductive success and timing
  • Certain genetic and environmental factors can influence the extent of devernalization and its impact on flowering
• Cold tolerance of plants


  A plant's ability to survive and thrive in cold temperatures
• Cold-tolerant plants


  • Often have mechanisms to continue growing even in chilly conditions, such as adjusting their metabolism to function efficiently at lower temperatures
• Seed dormancy


  A state of inhibited growth and metabolism in viable seeds, which prevents them from germinating even under favourable conditions
• Types of seed dormancy

  • Physiological dormancy
  • Physical dormancy
  • Morphological dormancy
  • Combined dormancy
• Germination


  1. Water uptake

  2. Activation of metabolic pathway

  3. Radicle emergence

  4. Cotyledon emergence

  5. Shoot development
• Bud dormancy


  The period when buds of perennial plants cease growth and remain inactive, typically during winter or unfavorable conditions
• Methods of breaking bud dormancy

  • Chilling treatment (cold stratification)
  • Photoperiod
  • Utilizing growth-promoting hormones
  • Altering temperature conditions
• Reasons for bud dormancy

  • Environmental stress
  • Seasonal changes
  • Genetic regulation
  • Resource allocation
  • Protection from damage