With the increase in concentration of applied salicylic acid (SA), chlorophyll (Chl) content decreased significantly in both wheat and moong seedlings. Chl a/b ratio decreased significantly only in wheat and remained constant in moong. On the other hand, total carotenoid (Car) content, size of xanthophyll pool, and de-epoxidation rate increased significantly with an increase in SA concentration in both plant species. Hence SA treatment may induce Car biosynthesis in these plant species, but the increase in the xanthophyll pool and de-epoxidation rate indicates that SA may create oxidative stress the degree of which is different in various plants. and S. T. Moharekar ... [et al.].
Arabidopsis thaliana L., ch1-1 (chlorophyll b-less mutant), gi-1 (GI deficient mutant), cry2-1 (blue-light-photoreceptor CRY2 deficient mutant), and Columbia (Col; wild ecotype) were grown under broad range of irradiances (I) from the beginning of germination and the effect of I on the survival, development, and flowering was studied. Under low and moderate I (<300 µmol m-2 s-1), flowering time and plant size at flowering showed great variations among ch1-1, gi-1, cry2-1, and Col, whereas under higher I (>500 µmol m-2 s-1), these characteristics were almost the same. Hence under high I, development and flowering of ch1-1, gi-1, cry2-1, and Col converged to almost the same state. Flowering time was negatively correlated with I, and under high I acclimation in A. thaliana was associated with a decrease in chlorophyll (Chl) content and increases in xanthophyll cycle pool and membrane-bound APX activity (EC 1.11.1.11) suggesting that an increase in oxidative stress induces earlier flowering. The plants of gi-1 and cry2-1 survived but Col and ch1-1 died under 1 000 µmol m-2 s-1, showing that mutants deficient in GI or CRY2 are more photo-stress-tolerant than Col and the Chl b-less mutant. Hence high I promotes in plants of Arabidopsis raised from germination till flowering the development and flowering time involving modulation of the photosynthetic apparatus, and this promoting effect is independent of the functions of flower-inducing GI or CRY2 gene. This can be regarded as photo-acclimation of A. thaliana for survival and reproduction under high I. and S. Moharekar ... [et al.].
The response of Picea glehnii, a cold-tolerant species in the boreal zone, to air temperature (T) was investigated for its cold-acclimated needles (i.e. the ones subjected to gradual decrease in T) and nonacclimated needles (i.e. the ones subjected to a sudden decrease in T) were compared under low temperature.
Cold-acclimated needles showed a greater increase of zeaxanthin and lutein contents than nonacclimated ones, whereas the nonacclimated needles showed a greater increase of thylakoid-bound ascorbate peroxidase (tAPX) activity than cold-acclimated ones under chilling conditions (after cold acclimation). These results suggest that: (1) low T induces the increase of zeaxanthin and lutein content, and tAPX activity; (2) accumulated zeaxanthin and lutein protect needles from photooxidative stress by dissipating excess energy before the reactive oxygen species (ROS) are formed in response to a gradual decrease in T (with cold acclimation and subsequent chilling condition), and by tAPX scavenging ROS formed in the case of a sudden decrease in T (without cold acclimation and chilling condition). and J.-J. Bae ... [et al.].