Spikelet Positions Research Articles

The Vascular System of the Wheat Spikelet

The attachment region of a mid-spike spikelet was sectioned serially. These sections were used to construct an accurate 3-dimensional model of the course of the vascular system that supplies the organs of the a and b florets, and the rachilla of the c and d florets. All organs are interconnected by vascular tissue, but certain parts of the system are phloem-only. In particular, the supply to the groove bundle of the pericarp, widely held to be the most important pathway to the grain, is made via an annulus of phloem to which lemma, palea and lodicules have phloem-only connections. The vascular system is sufficiently different from the pattern encountered in vegetative nodes to warrant treatment sui generis. The relationships between different cell types need greater histological study, especially in the complex composite bundles. This analysis shows that bundle shape in cross-section and the arrangement of xylem and phloem vary sharply over very short distances (100 ~ m ) .T he distribution of xylem and phloem transfer cells agrees with the proposal that significant solute relocation takes place in the regions where the vascular supplies to different organs meet. The area in the ovary neck that encompasses the fusion zone of the supplies to lemma, palea and pericarp emerges as a zone in need of detailed study, both in spikelet positions within a cultivar of known, but different, grain performance, and as a region to analyse for inter-cultivar comparisons.

A comparison of spring barley grown in England and in Scotland. 2. Yield and its components

SummaryYields of two spring barley varieties, Golden Promise and Maris Mink, were greater at the Scottish Plant Breeding Station (SPBS) than at the Plant Breeding Institute (PBI) in both 1976 and 1977. In both seasons more ears per plant were produced and the number of grains per ear was greater at the SPBS. Weight per grain was greater at the Scottish Plant Breeding Station in both 1976 and 1977, but the distribution of grain size along the ears differed between seasons. Grain at the tip of the ears of plants grown at SPBS in 1976 was lighter than the corresponding grain on the Cambridge-grown plants. In 1977 the SPBS-grown plants had heavier grains at all the main shoot spikelet positions. At the SPBS the relative difference between main shoot and tillers 1 and 2 was smaller than at the PBI.These results are taken to indicate that the combination of climatic factors in Scotland affects plant development in such a way that intraplant competition is reduced and more spikelet primordia survive to form grains and more tillers produce fertile ears.

Development of the Rice Panicle : I. Characteristics of the growth of spikelets at different positions on panicle

This study was undertaken to elucidate the growth process of young panicle of rice. The growth of each spikelet was investigated in relation to the positional differences and was compared with that treated with thinning and top-dressing at the end of spikelet differentiation stage (16 days before heading). Three spikelet positions, the upper (T-1), the middle (M-2) and the lower (B-2'), were selected for this experiment (Fig. 1a, b). The results obtained are summarized as follows: 1. In controls, the length of lemma, empty glumes and the width of spikelet at maturation decreased on lower position. But there was little differences in the length of anther and pistil, and the diameter of pollen among the spikelets at different positions on panicle (Fig. 2, Table 3 and 4). 2. The growth of each spikelet proceeded succesively from the upper to the lower position on panicle (Fig. 3). 3. Interrelationships of the growth of each spikelet organ were almost the same in all spikelets on panicle. Lemma, anther and pistil in a spikelet began to grow simultaneously. Marked growth occurred in lemma from 16 to 8 days before flowering, in anther and pistil from 16 to 3 or 2 days before flowering, and in the width of spikelet from 16 to 6 days before flowering (Fig. 4). 4. Regardless of spikelet position on panicle, meiosis of pollen was found to occur in the anther of the same length. However, the lemma length at meiotic stage in the upper spikelet was different from that in the lower one. Meiosis of the upper spikelet occurred when it was smaller than the lower spikelet (Fig. 2 a, c). 5. When the nutritive conditions were improved by thinning and top-dressing, the length of panicle, the number of spikelet, the length of primary branches and the diameter of rachis increased. The increase of the spikelet number was due to the decrease of degenerative spikelets (Table 1 and 2). 6. The lemma length of middle and lower spikelets, the length of empty glumes and pistil of all spikelcts, were increased by the treatment. The anther length and the pollen diameter in all spikelets were not increased and the growth period of anther in the lower spikelet was shortened by the treatment. The growth of the upper spikelet was not promoted by the treatment (Fig. 5, Table 3 and 4). Thus, the spikelet organs, which seemed to be differentiated in various manner from the apex, showed the different responses to the treatment. From these results, it is assumed that the positional differences in the spikelet growth were not only dependent upon the distribution of translocated substances but also upon the physiological specificity of each organ of the spikelet.

A Study of Floret Development in Wheat (Triticum aestivum L.)

Plants of wheat (Triticum aestlvum L.) cv. Aotea were grown at high or low nitrogen levels and in a natural photoperiod or continuous light. Starting 17–21 days from the double-ridge stage, eight plants from each treatment were sampled every 3 days until anthesis, and the two basal, the sixth, and the terminal spikelets were sectioned longitudinally. A developmental score was assigned to each floret and rates of development calculated. Continuous light hastened development but reduced the number of spikelets per ear, while high nitrogen delayed development but increased spikelet numbers. The number of florets initiated in each spikelet varied within narrow limits, but grain setting depended strongly on spikelet position and on treatment. Although florets were initiated in acropetal succession, the rate of development tended to increase up to floret 4 but then declined markedly. As a result grain setting was confined to basal floret positions, although the two basal spikelets developed so slowly that they contributed relatively little to grain yield. Distal florets degenerated almost simultaneously at or before ear emergence, but those in intermediate positions continued to develop until after fertilization in the lower florets. It is argued that the spikelet is an integrated system in which correlative mechanisms play a part throughout the development of the florets.