The Potential Pre-anthesis and Post-anthesis Contributions of Stem Internodes to Grain Yield in Crops of Winter Barley

Field experiments to assess the development of the main stem,its constituent internodes, and their potential contributionsto grain yield in one cultivar of winter barley were carriedout in four growing seasons. Internodes developed sequentiallyup the stem and all reached their maximum mass after attainingtheir final length. Lower internodes were the main potentialcontributors of pre-anthesis assimilate to grain-filling butupper internodes were an important source of stored assimilateaccumulated after anthesis. If the contribution of stored assimilateto grain yield is equated only with the potential pre-anthesiscontribution then the importance of the stem as a storage organis grossly underestimated. The ratio of pre-anthesis to post-anthesiscontribution to total storage ranged between years from 1:1·3to 1:3·1. Crops that lost more mass from the stem alsohad greater grain yields. The stem is the major source of assimilatetowards the end of grain-filling. Mass lost from the stem betweenthe time of maximum stem mass and maturity can potentially accountfor 62% to 92% of the increase in grain mass during this period. Pre-anthesis storage, Post-antheses storage, winter barley, Hordeum Sativum Lam, stem, internode, grain yield     

Effects on the Stem of Winter Barley of Manipulating the Source and Sink during Grain-filling: I. CHANGES IN ACCUMULATION AND LOSS OF MASS FROM INTERNODES

Source and sink activities of field-grown barley plants weremanipulated by shading the whole plant or by de-earing at varioustimes after anthesis. The changes in the masses of the internodes,ears, grains and leaves were followed until the grain matured. Shading reduced the mass of ears and grains and, in addition,shading to 45% of incident radiation from anthesis preventedmature internodes from increasing in mass. Severe shading (to9% of incident radiation) from 11 d after anthesis caused thenormal decrease in mass of internodes to occur earlier thanin unshaded plants. Thus, only assimilate in excess of thatrequired for tructural growth was stored in internodes. Lowerinternodes of plants shaded from anthesis lost more of the massthat had been accumulated prior to anthesis than control plants,giving a greater potential pre-anthesis contribution to grainyield. Internodes from plants that were de-eared accumulated more massthan internodes of control plants in one year but not in another,i.e. the potential for internodes to store assimilate appearsto be exploited in some years but not others. The mass of internodesfrom de-eared plants either decreased after that of controlplants or their mass stayed constant. De-eared plants had anincreased number of tillers compared with control plants; thesetillers could have been an alternative sink for assimilate storedin the internodes of de-eared plants. Mobilization of assimilate from internodes is in response todemand for assimilate from grains being in excess of currentphotosynthesis. Key words: Winter barley, stem reserves, mobilization, shading, de-earing     

Effects on the Stem of Winter Barley of Manipulating the Source and Sink during Grain-filling: II. CHANGES IN THE COMPOSITION OF WATER-SOLUBLE CARBOHYDRATES OF INTERNODES

Field-grown barley plants were manipulated by removing earsand by shading to promote and to reduce, respectively, the storageof carbohydrates in their stems. Water-soluble carbohydrate(WSC) was extracted and separated by HPLC into glucose, fructose,sucrose, and fructan of degree of polymerization (DP) 3, 4,5, > 5, and measured in both the penultimate and fourth internodesfrom the ear to determine the effects of the manipulations. During the accumulation of WSC, the mass of fructan with a DPgreater than 5 continued to increase whilst the mass of fructansof DP 3 to 5 reached a maximum and then remained constant. Fructanaccumulated in internodes while they were extending althoughmost of the fructan in an internode accumulated after it wasfully extended. When WSC was mobilized from the stem, the massof glucose, sucrose and fructan decreased but the mass of fructosefirst increased then decreased, indicating that fructan washydrolysed at a faster rate than its product, fructose, couldbe utilized. Plants shaded to 50% of incident light from 14 d after anthesisaccumulated the same mass of WSC in the stem as controlplantsin one crop, whereas in another crop, plants shaded to 9% ofincident light from 11 d after anthesis accumulated less WSCthancontrol plants. WSC in the stem was lost from the more intenselyshaded plants earlier than from control plants. Plants de-eared at anthesis and at 21 d after anthesis accumulateda similar mass of WSC to control plants, although plants de-earedat 9 d after anthesis, in another crop, accumulated a greatermass of WSC than control plants. Although control plants mobilizedalmost all of their stored WSC, de-eared plants retained 43–55%of the WSC stored in their penultimate internode and did notlose any stored WSC from their fourth internode. In the penultimateinternodes of de-eared plants the mass of glucose, sucrose andfructan decreased and this was balanced in part by an increasein the mass of fructose. In the fourth internode, the mass ofWSC remained constant but the mass of accumulated fructose wasequal to the decrease in the mass of fructan. Results are discussed in relation to current knowledge of fructanmetabolism and to contributions of stored WSC to grainyield. Key words: Winter barley, water-soluble carbohydrate, fructan, de-earing, shading     

Biology of suckers: late-formed shoots in sugarcane

Suckers in sugarcane are tillers that form late in the growing season after the population of main stalks has been established. Their biology has rarely been studied, though unsubstantiated comments relating to their morphology, development and number are abundant. In this paper, the literature is reviewed and new experiments presented. Comparison of suckers, emerging plant and ratoon cane showed that suckers have a different leaf and stem morphology. Suckers have a greater diameter at their stem base and shorter and wider leaves than primary stalks of a similar age. In 1 ‐year‐old crops, suckers have been demonstrated to decrease the net sucrose concentration of harvested material by diluting sucrose in the main stalks. By comparing main stalks without suckers to those that have initiated suckers, evidence is presented that suckers may also be decreasing the sucrose content of the stalks from which they are growing. Genotypic and environmental factors influence sucker number. Several experiments were designed to identify environmental stimuli for suckering. Increased nitrogen, through application late in the growing season, was found to increase the numbers of suckers present. Manipulation of the light environment of main stalks showed that a change in light quality (but not necessarily quantity) stimulated suckering. Further work is underway to define how these environmental stimuli lead to sucker initiation and growth. Major scientific questions that should be addressed are: the identification of other potential environmental stimuli, how the signals are perceived and translated into sucker initiation, and why suckers have different morphology. The practical challenge is to combine the new information about sucker biology and develop from it strategies to alter agronomy and select new cultivars that results in decreased suckering.     

Changes of enzyme activities associated with the mobilization of carbohydrate reserves (fructans) from the stem of wheat during kernel filling

Wheat plants were grown at a day/night temperature of 18/13°C under glasshouse conditions. Twenty-two d after anthesis, one set of plants was shaded to 50% of the normal photon fluence rate, another was 'degrained' by selective spikelet removal which left only the grains in the five central spikelets; a further set was left as control. Individual plants were harvested at days 22, 30 or 42 after anthesis. Extracts from the peduncle and the penultimate internode were prepared to determine the activities of sucrose phosphate synthase, sucrose synthase, fructan exohydrolase and acid invertase, and to assess the concentration of hexose sugars, sucrose and fructans. Measurements were also made of ear and individual grain weights, and stem f. wt and d. wt. There was a decline in the amount of fructans with time, more pronounced in 'shaded' (source-limited) than in control plants. By contrast, in 'degrained' (sink-limited) plants, the amount of fructans in the stem initially rose, then decreased, with a concomitant increase in the amount of fructose. The shifts in sugar content of the wheat culm reflected both the sink demand of the ear and source activity. The activity of fructan exohydrolase correlated with the carbohydrate changes. Under limited photosynthate assimilation, the mobilization of fructans from the internodes towards the ear was related to an increase in this enzyme, whereas the other enzymes played a less direct role in the mobilization of fructan reserves from the wheat stem.