The effect of indole-3-acetic-acid on the photosynthetic apparatus of Sinapis alba

Regulation of chloroplast development and function by cytokinin

A role of the plant hormone cytokinin in regulating the development and activity of chloroplasts was described soon after its discovery as a plant growth regulator more than 50 years ago. Its promoting action on chloroplast ultrastructure and chlorophyll synthesis has been reported repeatedly, especially during etioplast-to-chloroplast transition. Recently, a protective role of the hormone for the photosynthetic apparatus during high light stress was shown. Details about the molecular mechanisms of cytokinin action on plastids are accumulating from genetic and transcriptomic studies. The cytokinin receptors AHK2 and AHK3 are mainly responsible for the transduction of the cytokinin signal to B-type response regulators, in particular ARR1, ARR10, and ARR12, which are transcription factors of the two-component system mediating cytokinin functions. Additional transcription factors linking cytokinin and chloroplast development include CGA1, GNC, HY5, GLK2, and CRF2. In this review, we summarize early and more recent findings of the long-known relationship between the hormone and the organelle and describe crosstalk between cytokinin, light, and other hormones during chloroplast development.

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO2 exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA3) at the concentration of 25 μg/1 (GA-plants), and then grown under 17 W/m(2) blue light (B-plants) or 11 W/m(2) red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA3 suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.

The influence of brassinosteroid on growth and parameters of photosynthesis of wheat and mustard plants

The growth response of wheat (Triticum aest. L.) and mustard seedlings (Sinapis alba L.) treated with 10(-6) mol · l(-1) brassinosteroid (BR) foliar spray was measured. BR-treatment resulted in a general promotion of plant growth. We found the accumulation of photosynthates to be stimulated in the treated plants, as indicated by enhanced fresh and dry weights of leaves and shoots. BR also promoted the synthesis of soluble proteins and soluble reducing sugars, whereas the chlorophyll content was hardly affected. CO(2)-fixation in vivo as well as the (in vitro) RubPC-ase activity of BR-treated leaves were enhanced. In the developing wheat leaves we detected no difference in the ratio fraction-I-protein (F-I-P)/total soluble protein between BR-treated and control plants whereas in the expanded leaves this ratio was lowered under BR-treatment.

Cytochemical localization of photosystem II donor sites

Tetramethylbenzidene, an artificial donor of electrons to the photosystem (PS) II reaction center, is oxidized to an osmiophilic polymer that allows for the localization of the donor site of PS II. Mesophyll chloroplasts of Sorghum bicolor (L.) Moench. contain 0.1-0.2 micron deposits only in the grana stacks and on the lumen side of the thylakoid. Agranal mature bundle sheath plastids (known to be devoid of PS II activity) show little deposition and the products appear randomly distributed along the lamellae. The cytochemical localization of PS II donor sites on the lumen side is consistent with flash photolysis and diaminobenzenesulfonic acid inactivation studies as well as the chemiosmotic theory for the generation of a proton gradient.