Whole Plant Senescence of Sunflower Following Seedhead Removal

Abstract

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 ...

Escalation of Growth and Yield in Mungbean by Sink Manipulation: An Approach for Minimizing Pod Picking Episode

“…Overall, it appeared that deflowering at later stage increased total dry weight in all deflowering treatments in both the years and followed increasing pattern as 35 DAS< 55 DAS< 70 DAS. Deflowered sunflower plants had a larger stem and leaf dry weight, according to previous research of Ho and Below (1989). In accordance with their findings, deflowering effect in the present study showed increased total dry weight in comparison to control (NDF) (Figure 1).…”

Whole Plant Senescence: Reproduction and Nutrient Partitioning

“…Both head removal and the growing environment influenced the process of leaf senescence (Ho et al 1987). It was shown that while the absence of seeds affected partitioning and the rate of assimilation, as well as extending the period of assimilation of dry matter, reduced nitrogen and phosphorus, the total accumulation was the same in headed and deheaded plants (Figure 8.7) (Ho and Below 1989). Deheading led to accumulation of photosynthate and minerals in the vegetative tissues, while intact plants allocated large portions of nutrients to the seedhead.…”

“…In soybean (Glycine max), overall senescence of the leaves follows seed production. Removal of the flowers and fruits delayed senescence, but when reproductive structures were removed early in their development, a greater delay occurred than when older fruits were removed (Leopold et al 1959 Vegetative tissues become alternate sinks for nutrients after deheading, which delays senescence (data from Ho and Below 1989, 1983a. The leaves of continuously depodded (de-sinked) soybean plants, although dark green, showed lower photosynthetic rates than the yellowing leaves of the senescing control plants.…”

The capture and gratuitous disposal of resources by plants

“…Rousseaux, Hall & Sánchez 1993). Experiments in which grain set was prevented demonstrated a consistent delay and/or slowing down of leaf senescence in oilseed species, including sunflower and soybean (Ho & Below 1989; Lindoo & Noodén 1977). In cereals, on the other hand, ear removal may delay or accelerate leaf senescence, depending on genotype (Thomas & Smart 1993).…”