Diurnal regulation of plastid genes in Populus deltoides.

Light regulates leaf and chloroplast development, together with overall chloroplast gene expression at various levels. Plants respond to diurnal and seasonal changes in light by changing expression of photosynthesis genes and metabolism. In Populus deltoides, a deciduous tree species, leaf development begins in the month of March and leaf maturation is attained by summer, which is subsequently followed by autumnal senescence and fall. In the present study, diurnal changes in the steady state transcript levels of plastid genes were examined in the fully developed leaves during summer season. Our results show that steady state level of the psaA/B, psbA, psbEFLJ and petA transcripts showed differential accumulation during diurnal cycle in summer. However, there was no significant change in the pigment composition during the day/night cycle. Our studies suggest that the diurnal regulation of steady state mRNA accumulation may play a crucial role during daily adjustments in plants life with rapidly changing light irradiance and temperature.

Effect of light intensity on in vitro multiple shoot induction and regeneration of cotton (Gossypium hirsutum L. cv Khandawa-2).

Cotyledonary nodes taken alongwith shoot apex from seedlings of cotton (G. hirsutum) proliferated into shoots on nutrient agar medium supplemented with cytokinins. In the presence of optimal plant growth regulators, low light intensity enhanced the number of shoots initiated per explant in cotton. An average of 33.5 +/- 2.9 shoots were obtained from a single explant cultured for 8 weeks which is about four fold higher than the values reported in earlier protocols. The isolated shoots were rooted on nutrient agar medium supplemented with alpha-naphthalene acetic acid and transferred to soil after acclimatization. Regenerated plants were morphologically identical to the seed-germinated plants and were fertile.

Uncoupling of photosystems during light dependent dinitrogen fixation by a non-heterocystous cyanobacterium Plectonema boryanum.

Plectonema boryanum grows under microaerobic nitrogen starvation conditions by temporal separation of the oxygen-sensitive nitrogen fixation and the oxygen-evolving photosynthesis. During the nitrogen-fixation phase, depression in light-dependent oxygen evolution results from alterations in the stare of QA/QB complex. The reaction centre in photosystem II is not oxidised efficiently. Light dependence of nitrogenase function under such conditions appears to be related to the coupling of photosystem I to endogenous electron donors, such as glycollate. This cyanobacterium provides a natural example of in vivo shift in coupling between the photosystems during nitrogen-fixing growth.