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191.
Air-grown tobacco (Nicotiana tabacum L.) plants were transferred for one week into a low oxygen atmosphere (2 kPa O2, LO) to study both immediate and long-term effects of the suppression of photorespiration on net photosynthetic rate (PN), plant morphology, and chloroplast ultrastructure. The PN and the leaf conductance for CO2 increased upon exposure of attached tobacco leaves to LO. These results may suggest that under LO, external CO2 is used to consume the radiant energy normally utilized in photorespiration by net CO2 assimilation at the expense of an increased rate of transpiration. The increase in the coefficient of nonphotochemical fluorescence
quenching indicates that under LO, (surplus) radiant energy is also dissipated as heat. Prolonged LO-treatment of tobacco
resulted in a decrease in the PN (measured in air) and in a reduction in the number of starch grains in the chloroplasts. Concomitantly, large lipid globuli
appeared in the chloroplasts and the distance between the thylakoids forming the grana decreased. These changes in the ultrastructure
of chloroplasts may have contributed to the decline in the PN. The LO-treated plants were considerably smaller than the control plants maintained in air. This appears to have resulted
from a reduction in the rate of leaf area expansion at the expense of an increase in the specific mass of the leaves. This
long-term response to LO-treatment may allow the plants to conserve water.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
192.
H A W?sten R Bohlmann C Eckerskorn F Lottspeich M B?lker R Kahmann 《The EMBO journal》1996,15(16):4274-4281
Ustilago maydis, a fungal pathogen of corn, can alternate between yeast-like and filamentous growth. This dimorphic switch is governed by the mating-type loci. We have identified an abundant class of small SDS-insoluble cell wall proteins, designated repellents, specifically present in the filamentous form. Genetic analysis revealed that these peptides are processed from a single precursor protein, Rep1. Rep1 comprises 652 amino acids with a leader sequence for secretion. A characteristic feature of Rep1 is 12 repeats of a 37 amino acid consensus sequence; 10 of these repeats are separated by Kex2 protease cleavage sites. In (delta)rep1 mutants formation of aerial hyphae and surface hydrophobicity were reduced dramatically. This and the fact that expression of rep1 is regulated by the mating-type loci indicates that repellents play a structural role in the formation of aerial hyphae. 相似文献
193.