The usefulness of using the ehloroplast number in epidermal guard cells as an indirect ploidy indicator was evaluated on seed-grown and tissue culturederived maize plants. For seed-grown plants, two maize genotypes (B89 and R75) which had both diploid and tetraploid seeds available were used as experimental materials. The ploidy levels of seedgrown plants were confirmed by flow cytometric analysis of nuclear suspensions from these plants. For regenerated plants, haploid and diploid levels were examined and the ploidy levels of these plants were determined by chromosome counts of cells from root tips. A positive relationship between the chloroplast number and ploidy level was observed for both seed-grown and regenerated plants. The stomatal guard cells of tetraploid plants had nearly double the number of chloroplasts as the diploid plants. Similar results were found from the regenerated plants. The differences in the mean chloroplast number between diploid and tetraploid seed-grown plants and between haploid and diploid regenerated plants were highly significant. The results of this study demonstrate that counting chloroplasts m guard cells can be an efficient means of screening a large number of plants for ploidy levels. In addition, this study suggests the possibilities of using this method for detecting contaminated seed lots by different ploidy seed and for distinguishing plants of different genotypes.

Greenhouse and field studies examined the effect of flower or seedhead removal on leaf senescence and associated changes in sunflower (Helianthus annuus L.) plants. At intervals during seed development, selected leaves (leaves 6 through 8 from the top in the greenhouse and leaf 7 from the top in the field) were harvested and analyzed for chlorophyll, specific leaf weight, N, P, soluble protein, and electrophoretic gel profiles of soluble polypeptides. In both the greenhouse and the field, the leaves of headless plants retained or accumulated more N, P, soluble protein, and dry weight than leaves of plants with heads. Obviously, head removal affected the partitioning of these metabolites during seed development. None of the treatments resulted in the formation of new polypeptides (electrophoretic gel profiles). Comparisons of the rates and extent of loss ofchlorophyll, soluble protein, and polypeptide bands (especially ribulose 1,5-bisphosphate carboxylase) from the leaves of headed and deheaded plants showed that head removal delayed the rate of development of leaf senescence for the greenhouse-grown but had much less effect on fieldgrown plants. These findings illustrate the variability in different parameters commonly associated with the leaf senescence processes of headed and deheaded sunflower plants grown under different environments.Senescence has been described as the natural deteriorative process leading to death of an organ or organism (12). This process is complex, controversial, and not well understood, especially with respect to the causal factor(s) (26). Additional information concerning the cause, course, and control of senescence is of agronomic importance because of the high positive correlation between leaf area duration and grain yield (9).There are no comprehensive theories of senescence (13) depodding resulted in de novo synthesis of four polypeptides (30), he concluded that depodding altered leaf function (became a sink) rather than delaying or preventing senescence. CraftsBrandner et al. (7,8) reported similar results from depodding soybean plants (cv Harosoy), except that RuBPCase was only initially lower in the leaves of depodded plants. By maturity, the depodded plants had accumulated as much dry weight (net photosynthesis) and N in the above ground parts as the podded plants. Apparently the presence of pods only altered the partitioning of plant constituents (7). Based on the seasonal profiles ofChl, and activities ofthe functional enzymes nitrate reductase, nitrogenase and RuBPCase, the initiation of leaf senescence was similar for podded and depodded plants (7,8).Although Moss (17) reported that the prevention ofpollination (ear bagging or removal) delayed senescence in maize, other workers (1,3,25) found such treatments accelerated leaf and plant senescence. Subsequent work (5, 6, 27) resolved this conflict by showing the response was a reflection of genotype. A detailed comparison of such divergent genotypes (5, 6) permitted the conclusion that the ear per se does not fully...

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This study was undertaken to further clarify the relationship between seed development and monocarpic senescence of sunflower (Helianthus annuus L.). Field-grown plants with and without seedheads were evaluated for rate and duration of accumulation of dry weight, reduced N, and P by whole shoots, and for partitioning of these constituents within the individual plant parts.Concurrent with seedhead removal, ['5N]nitrate was applied to the plants in a selected area of the experimental plot. Whole plants (above ground portions) were harvested seven times during the seed-filling period and analyzed for dry weight, reduced N, and P. Although seedhead removal depressed the rates of dry weight, reduced N, and P accumulation by whole shoots, it extended the duration of accumulation of these constituents, relative to headed control plants. As a result, the final whole shoot dry weight and N and P contents at seed maturity were similar for deheaded and headed plants. Seedhead removal also affected the partitioning of dry matter, reduced N, and P but the relative proportions varied as a function of constituent and growth stage. Analysis of 15N present in whole shoots at physiological maturity showed that similar amounts of nitrate were absorbed during the postflowering period by headed and deheaded plants.These data indicate that the absence of seeds does not affect the total accumulation of dry matter, reduced N, or P, by sunflower plants, but does alter the rates of accumulation and partitioning of these constituents.Senescence can be viewed as a series of degenerative processes that lead to diminished metabolic activity and ultimately plant death. While the cause of plant senescence remains elusive, development of reproductive structure(s) has long been implicated (16,20 (8) reported that pod removal had no effect on the magnitude or rate of accumulation of dry matter (net photosynthesis) or reduced N by whole shoots. In podless soybean plants, the accumulation of these constituents in leaves and stems completely compensated for lack of seeds (8). Recently, the relationship between developing seeds and senescence of soybean has been further complicated by reports ofcultivar differences in the rate of photosynthesis and carboxylase activity following pod removal (10).For maize, ear removal (or prevention of pollination) has been reported to accelerate, have no effect, or to delay leaf senescence with the divergent responses being associated primarily with genotype (3,6,7,21,22). Regardless ofsenescence type, ear removal results in an earlier decline in leaf carbon exchange, but at different rates for different genotypes (5, 1 1). Although buildup of carbohydrates (1, 3) or accelerated loss of leaf nitrogen (4) have been implicated as causal factors of ear-removal-induced leaf senescence, evidence to support either mechanism is not convincing. With regard to whole plant senescence, studies with maize have shown that, regardless of senescence type, ear removal results in a significant decrease in net photosynthetic ...