ICAR AIEEA PG 2024 - Agronomy

(A) Photo-acclimation (or photosynthetic acclimation) is the phenotypic adjustment made by plants in chlorophyll content, photosystem stoichiometry (PSI/PSII ratio), and Rubisco content to optimize light harvesting and carbon assimilation in response to changing light intensity.

• Gibberellic acid ($GA_3$) is a potent germination promoter. It stimulates the aleurone layer of seeds to synthesize $\alpha$-amylase, hydrolyzing endosperm starch into simple sugars to nourish the growing embryo.
• Coumarin, phthalides, and phenolic compounds like ferulic acid act as germination inhibitors promoting seed dormancy.

• Vernalization is strictly an aerobic process. It requires metabolically active cells with sufficient oxygen supply and respiratory substrates (carbohydrates) to synthesize vernalin / promote epigenetic flowering competence.
• Under anaerobic conditions (absence of $O_2$), chilling temperatures fail to induce vernalization.

• The Electro-osmotic theory for phloem transport was proposed by D.S. Fensom (1957) and D.C. Spanner (1958).
• It postulated that an electric potential difference across sieve plates, driven by active circulation of potassium ($K^+$) ions, drives the electro-osmotic flow of water and sucrose solution through sieve pores.

• Sucrose is the predominant non-reducing disaccharide translocated in the phloem of higher plants, along with raffinose-family oligosaccharides (RFOs: raffinose, stachyose) in symplastic polymer-trapping species.
• Reducing monosaccharides such as glucose and fructose are not major phloem mobile sugars.