Within each mango (Mangifera indica L.) tree there is a diversity in flowering ability among its terminál branches. Significant variations in net photosynthetic rate (Pn), transpiration rate, stomatal conductance (gj) and mesophyll efficiency (mesophyll capacity to fix CO2) were observed generally among the productive branches. However, the extent of variation was more pronounced in trees with irregular bearing habits (cv. Langra) as compared to regular bearers (cv. Romani). In generál, correlation coefficients indicated that variations in among n5 branches were mainly due to the mesophyll efficiency and g^, In regular bearing trees, the narrow range of variation in was related to a better mesophyll capacity. This in tum might result in higher carbon build-up of 05 branches which would háve helped them to flower regularly with minimum branch to branch variations.
A brief pulse' of red (R) radiatíon increased actívity and protein content of phosphoenolpyruvate carboxylase (PEPC): diis increase was inhibited by cycloheximide. The efifect of R was far-red pulse (FR) reversible when R was followed inunediately (but not after 24 h) by FR. Thus phytochrome was involved in PEPC regulatíon in etiolated maize leaves. Both a lag phase and a saturation exist in the process of R induction of PEPC synthesis: the highest PEPC acitívity was obtained 24 h after R. Etiolated maize leaves of different age showed different sensitivity to R: the highest sensitivity was found in 5 d-old seedlings. 5 min of R was sufficient for inducing PEPC synthesis, and no additíonal increases were obtained in actívity and protein content of PEPC when the R tíme was prolonged.
The Chemical weed control should apply herbicides which interfere only with the plant-specific processes, like photosynthesis, biosynthesis of pigments or essential amino acids. Accordingly, attention for herbicide development is focused on the chloroplast as a typical plant organelle. This páper reports on the mode of action of so-called bleaching compounds which affect the biosynthesis of carotenoids and chlorophylls, respectively, causing interrupted build-up or degradation of the photosynthetic apparatus. In the first čase such inhibitors lead to accumulation of precursors of P-carotene and xanthophylls, which cannot protéct chlorophyll (Chl) against the photooxidation. Herbicidal inhibitors of Chl biosynthesis result in accumulation of protoporphyrin IX which is sensitised by light thereby inducing radical peroxidative reactions. The peroxidative stress can - under certain circumstances - be counteracted by the antioxidative systém of the plant cell. Basic biochemical studies and molecular genetics in this field of herbicidal inhibitors research are briefly outlined.
During the vegetation period from June to October 1990 the growth, photosynthetic C02-fixation, pigment content and chlorophyll (Chl) fluorescence characteristics were compared in the needles of 5-year-old spruce dones Picea abies (L.) Karst., cultivated for two years on the soil and the sand, with or without addition of minerál fertilizers. Minerál deflciency in the spruce dones grown on the sand instead of a humus containing soil resulted in somewhat reduced lengthwise growth of shoots and needles, lower level of Chl and carotenoids (Car), as well as lower net photosynthetic rates (F^) per needle area unit and in generál also lower stomata conductance (gH2o) values. In contrast, the variable Chl fluorescence measured via the Chl fluorescence decrease ratio (Rfj = fd/fs) was only little affected, indicating an intemal íunctional photosynthetic apparatus even under minerál deflciency with a lower Chl content. In fact, Fj,} expressed on Chl basis was even signiflcantly higher in the newly developed 1990 needles of the sand cultures than in the soil ones. Application of a forestry fertilizer with basic minerals (K, Ca, Mg and some N) to the sand cultures increased growth of shoots and needles, levels of Chl and Čar, F^ and stomata conductance, and decreased the Chl fluorescence ratio F690/F735 and lability of the photosynthetic apparatus, as also seen in increased values of the ratio Chl/Car (a+b/x+c). The hasič minerál elements are thus necessaiy for the photosynthetic apparatus development, as well as stability of its pigment content and physiological function.