Non-photochemical quenching of chlorophyll fluorescence (qN) and its three components (qNf, qNm, and qNs) in the flag leaves of wheat grown in the field were studied by a fluorometer PAM-2000 on clear days. The diurnal variation patterns of qN in just fully extended (JFEL) and aging leaves (AL) were similar, but qNm declined markedly in JFEL while it remained at a relatively high level in AL under strong sunlight at noon. Furthermore, at midday qNf was higher than qNs in JFEL, but much lower in AL. The results show the relative contributions of different mechanisms in preventing the photosynthetic apparatus from photodamage change during leaf development. and S.-S. Hong ... [et al.].
Ultrastructural changes in chloroplasts of primary leaves of 15-d-old bean plants (Phaseolus vulgaris L. cv. Cheren Starozagorski) in response to a single stress (increasing water deficit, WD) as well as to combined stress (WD plus high temperature, WD+HT) were investigated under the possible protective or reparatory effects of the carbamide cytokinin 4-PU-30 [N-(2-chloro-4-pyridyl)-N-phenylurea] applied before or after the stress. Essential structural changes in chloroplast ultrastructure occurred mainly in plants that had experienced WD+HT: the thylakoids were swollen, the envelope was destroyed, and the spatial orientation of inner membrane system was not typical. Changed starch accumulation was also observed. 4-PU-30 protected chloroplast ultrastructure under WD+HT. and D. Stoyanova. I. Yordanov.