Parameters of canopy architecture were related to light interception and productivity using data from a field experiment with corn grown at population densities from 17,500 to 125,000 plants per hectare. With nutrients and soil moisture nonlimiting, the amount of solar radiation intercepted by the foliage canopy was a major determinant of crop growth during the vegetative stage. Leaf arrangements with a preponderance of erect leaves, occurring just before the tassels emerged, allowed the deepest penetration of light into the foliage canopy and gave the highest crop growth rates. Computer simulation of photosynthetic production using the measured foliage display characteristics closely approximated measured rates of growth before anthesis. The yield of grain correlated well with crop growth rates up to an optimum population density, but then became negatively associated with density as further increases in the numbers of growing pouits apparently placed too great a demand on the community's metabolite‐producing ability.

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The mechanism(s) involved in the effect of Azospirillum brasilense strain Cd on root susceptibility to nodulation was studied in medic seedlings grown in pouches. The number of nodules above the position of the root-tip mark at the time of inoculation and the position of the uppermost nodule were used as parameters for determining the rate of nodule initiation. Cell-free extracts and culture supernatants prepared from Azospirillum and the cytokinin benzyladenine (10−9 M) significantly increased the number of nodules formed above the root-tip mark when applied together with Rhizobium compared with those formed with Rhizobium alone. The application of indoleacetic acid did not cause an increase in the number of nodules. In the absence of Rhizobium, exposure to Azospirillum at a concentration of 109 cfu/mL or to compounds excreted by the bacteria into the growth medium caused a 40% increase in endogenous ethylene production by the roots. A less concentrated inoculum did not increase ethylene production. Inoculation with Azospirillum significantly increased the specific activity of the enzymes glucose-6-phosphate dehydrogenase, L-phenylalanine ammonia-lyase, and shikimate dehydrogenase compared with roots inoculated with Rhizobium alone. Key words: Azospirillum, Rhizobium, Medicago polymorpha, root morphology, nodule initiation.

Leaf display in foliage canopies of equidistantly spaced corn plants was measured; the vertical distribution of leaf area within several angle classes are given at various stages ot growth for seven population densities. When used in computer simulations, these descriptions provide calculated light profiles which agree well with measured profiles. The canopies are compared with earlier and more general reports from other workers.

The damaging effects of UV-A irradiation on lens waterinsoluble a-crystallin, plasma membranous and cytoskeletal proteins derived from bovine lenses were studied. Young and adult bovine lenses were kept viable for 2 months in organ culture. After 24 h of incubation they were irradiated, and analyses of the proteins by one-dimensional and two-dimensional gel electrophoresis followed by Western blotting were carried out at several time intervals. RNA isolation, PCR and Northern blotting were also performed. We identified age-related changes in water-insoluble a-crystallin, the major membrane protein MP26 and the cytoskeletal proteins vimentin, phakinin and actin between control and UV-irradiated lenses. It appeared that adult lenses are more susceptible to UV light than young lenses, and protein modification occurred more frequently in adult lenses. UV-A irradiation affects not only the cytoskeletal structure, as deduced by the abnormal arrangement of actin in the fiber cells, but also leads to degradation of actin mRNA. Furthermore, analysis of the expression of hsp25 and hsp70 revealed some alteration in the protein pattern of adult lenses. We suggest that degradation of the cytoskeletal proteins following irradiation is due to, at least in part, the decreased protective ability of heat shock proteins upon aging.Keywords: a-crystallin; cytoskeletal proteins; lens aging; plasma membrane; UV-A irradiation.UV-A light (300±400 nm) penetrates the cornea and is maximally absorbed by the eye lens [1]. The human lens contains low molecular mass compounds which absorb maximally at < 365 nm [2] At this specific wavelength the lens is susceptible to irradiation. Experiments in organ culture of bovine lenses showed a relationship between UV-A radiation at 365 nm and subsequent lens opacity. It has been shown that epithelial enzymes of bovine lenses (ATPase, hexokinase, catalase and glucose-6-phosphate dehydrogenase), which are involved in metabolism and the defense mechanism against oxidation, are affected by UV-light [3,4]. Transglutaminase, which is a calciumdependent acyltransferase, may be involved in the mechanism by which UV-A causes damage to the eye lens [5]. The small heat shock protein aB-crystallin [6,7] and hsp25 [8] are substrates for the latter enzyme. We recently demonstrated that modifications, aggregation and reduced chaperone-like activity of water-soluble a-crystallin obtained from UV-A irradiated adult bovine lenses [9] affect lens transparency. This process may accumulate during aging.In this study we addressed the question of whether plasma membranous and cytoskeletal proteins from the water-insoluble fraction of young and adult bovine eye lenses are affected differently by UV-A radiation. The plasma membrane±cytoskeleton complex participates in the maintenance of lens shape, and both structures associate with lens crystallins [10]. We restricted our study to cytoskeletal proteins such as vimentin, phakinin (CP49), b-actin and the major lens membrane protein (MP26) which may be modified as a consequenc...

High oxygen load has a toxic effect on bovine lenses in organ culture. These effects appear to be cumulative: the higher the oxygen partial pressure and the greater the number of exposures, the more severe the changes observed in the lenses. Changes marking toxicity follow the route of oxygen diffusion into the lens, from the periphery to the center. Cautious interpretation of the results may indicate a role of oxygen (and/or its derivatives) in human cataract formation.

A novel experimental system was used to investigate the localized effects of microwave radiation on bovine eye lenses in culture for over 2 weeks. Using this setup, we found clear evidence that this radiation has a significant impact on the eye lens. At the macroscopic level, it is demonstrated that exposure to a few mW at 1 GHz for over 36 h affects the optical function of the lens. Most importantly, self-recovery occurs if the exposure is interrupted. At the microscopic level, close examination of the lens indicates that the interaction mechanism is completely different from the mechanism-causing cataract via temperature increase. Contrary to the latter's effect, that is particularly pronounced in the vicinity of the sutures and it is assumed to be a result of local friction between the edges of the fibers consisting the lens. Even if macroscopically the lens has recovered from the irradiation, microscopically the indicators of radiation impact remain.

Azospirillum brasilense Cd cell concentration of 105–107 colony-forming units (cfu)/mL applied 24 h before Rhizobium (106 cfu/mL), increased nodule formation in the non root hair zone, more than twofold, in pouch-grown Medicagopolymorpha and Macroptilium atropurpureum seedlings, compared with Rhizobium alone. The increase in nodule formation in pouch-grown Trifolium alexandrinum following preinoculation with Azospirillum was 20%. The percentage of nodulated seedlings rose from 0 to 25% when Medicago polymorpha was preinoculated with Azospirillum followed by the application of 10 cfu/mL Rhizobium meliloti, a level which by itself was not sufficient to initiate nodule formation. Acetylene reduction activity in Medicago polymorpha and Macroptilium atropurpureum seedlings after inoculation with Azospirillum–Rhizobium was markedly increased. A possible reason for the increased susceptibility to Rhizobium infection may be that Azospirillum stimulates the formation of a larger number of epidermal cells that differentiate into infectable root hairs.