Effect of Absence of Developing Grain on Carbohydrate Content and Senescence of Maize Leaves

Abstract

In maize (Zea mays L.) grown under normal conditions in Rhodesia, prevention of pollination or removal of the ears after flowering caused premature senescence of the leaves above the ear, preceded by the appearance of a purplish red color. In plants from which the ears had been removed the concentration of sugars and starch increased markedly in both upper and lower leaves, the increase being greater in the upper leaves.The removal of flowers or of developing fruits has been observed to delay senescence in a number of annual plants (5). In contrast, we have noticed in Rhodesia that the removal of developing ears causes leaves of maize plants to wither prematurely. Two experiments were conducted to investigate this problem. METHODSIn both experiments the locally bred single-cross hybrid 59H17, known commercially as SR52, was grown under normal conditions on fertile soil at a density of 31,000 plants per hectare (12, 500 plants per acre).In the first experiment, we investigated the effect of ear removal or prevention of pollination on leaf senescence. There were four treatments, viz., a control, ear removal 13 or 27 days after silk emergence, and covering the silks during the period of pollen shedding. Plots consisted of 10 plants in four replicates.At the time of flowering the area of every leaf was measured on 20 plants. Subsequently, the green, i.e., unwithered, leaf areas were estimated at weekly intervals until 8 weeks after flowering, and the green leaf area above and below the ear was calculated (1).In the second experiment we studied the effect of ear removal on carbohydrate accumulation. This experiment consisted of two treatments in three replicates, namely, a control and ear removal 19 days after flowering.Samples of leaf laminae were harvested from both above and below the ear on three occasions, namely, 7, 17, and 28 days after ear removal. Each sample consisted of 10 laminae, obtained by collecting either the middle two of the laminae above the ear, or the middle two of the laminae below the ear from each of five plants. Parts of some laminae had withered by the time of the third harvest, and these parts were discarded.The samples were always collected shortly before noon and within half an hour were placed in a forced draught oven at a temperature of 110 to 120 C for 20 min and then dried for about 6 hr at 60 to 70 C.The dried samples were finely ground and analyzed for total nonstructural carbohydrates with Clarase 300 (9). Since fructosans do not occur in maize (2), the results represent total sugars plus starch, expressed as glucose. In addition, reducing and nonreducing sugars were determined after extraction with alcohol (8); the replicate samples for the third harvest were analyzed separately, but for the first two harvests composite samples from the three replicates were used for the sugar determinations. Starch was calculated by difference: (total nonstructural carbohydrates minus total sugars) x 0.9. All analytical results are expressed as percentages of the dry matter. RESULTSExper...

Effect of Foliar Applications of Urea on Accelerated Senescence of Maize Induced by Ear Removal

“…ear removal) results in an acceleration of leaf and plant senescence, relative to eared control plants (1,3,4,5). Crafts-Brandner et al (4) found when visual symptoms of leaf senescence were apparent, rates of accumulation of dry matter (net photosynthesis), reduced N (nitrate assimilation) and P by the shoot decreased rapidly after ear removal and ceased by 30 d after anthesis.…”

Physiological observations of maize (Zea mays L.) genotypes differing in source-sink ratios

“…All defoliation treatments decreased the percent TNC of both stalk positions by 10 to 20 days after treatment. (Daynard et al, 1969;Hume and Campbell, 1973 Grain weight of control plants (Table 5) Concurrent with earlier senescence of leaves for most genotypes in 1979 was an increase in the days to physiological maturity and the grain Plants without ears exhibited a purple discoloration along the midrib and leaf margins similar to observations by Moss (1962) and Allison and Weinmann (1970). There was less purple discoloration with ear removal plus 50 percent defoliation than with ear removal and no defoliation.…”

“…Leaf export of assimilates Hartt, 1965) has been shown to decrease, whereas leaf sugar (Sayre et al, 1931;Allison and Weinmann, 1970;Hume and Campbell, 1973;Ciha and Brun, 1978) and leaf starch (Kollman et al, 1974) have been shown to Increase following sink reduction or removal.…”

Physiological observations of maize (Zea mays L.) hybrids differing in photosynthetic capability

“…High N has reduced phosphate uptake in maize in a pre vious study (Bennett et al, 1962); (2) poor sink development and feedback of assimilates. Where sink development was pre vented in maize, leaf CER has decreased due to feedback of assimilates and leaf margin purpling was reported (Allison and Weinmann, 1970;Moss, 1962). The high CER cultivars in this study have been observed to tiller profusely in field experiments (Part I above) but tillers were absent from these pot-grown plants.…”