Each perennial woody plant is a highly integrated system of competing carbohydrate sinks (utilization sites). Internal competition for carbohydrates is shown by changes in rates of carbohydrate movement from sources to sinks and reversals in direction of carbohydrate transport as the relative sink strengths of various organs change. Most carbohydrates are produced in foliage leaves but some are synthesized in cotyledons, hypocotyls, buds, twigs, stems, flowers, fruits, and strobili. Although the bulk of the carbohydrate pool moves to sinks through the phloem, some carbohydrates are obtained by sinks from the xylem sap. Sugars are actively accumulated in the phloem and move passively to sinks along a concentration gradient. The dry weight of a mature woody plant represents only a small proportion of the photosynthate it produced. This discrepancy results not only from consumption of plant tissues by herbivores and shedding of plant parts, but also from depletion of carbohydrates by respiration, leaching, exudation, secretion, translocation to other plants through root grafts and mycorrhizae and losses to parasites. Large spatial and temporal variations occur in the use of reserve- and currently produced carbohydrates in metabolism and growth of shoots, stems, roots, and reproductive structures. A portion of the carbohydrate pool is diverted for production of chemicals involved in defense against fungi, herbivores, and competing plants. Woody plants accumulate carbohydrates during periods of excess production and deplete carbohydrates when the rate of utilization exceeds the rate of production. Stored carbohydrates play an important role in metabolism, growth, defense, cold hardiness, and postponement or prevention of plant mortality.

Carbohydrate sources and sinks in woody plants

Pollination is a process that is vital for the survival not only of flowering plants, but also for mankind. Yet human efforts to manipulate the reproduction of crop plants have been largely empirical. Today, research into plant reproduction is not given high priority. Yet it provides the means of ensuring successful pollination, in order to maximize fertilization and hence crop production. The pollination process is susceptible to modification to permit the introduction of desirable genes, for example, for disease resistance, from wild species into crop plants. The potential applications are endless, yet all depend on a precise knowledge of the events of pollination (see reviews by STanley and LInskens 1974, FRankel and GAlun 1977, CLarke and KNox 1978).

Pollen-Pistil Interactions

Immediate and small-scale weather effects may act as constraints on pollination. A review of existing studies, mostly involving crops, reveals opportunities for research exploiting recent advances in microclimatic technique. Intrafloral temperatures are modified in “disc,” “bowl-shaped,” “microgreenhouse,” “hairy hgat trap,” “hanging bell,” and thermogenic flowers. Protection from free water or extreme humidities is achieved by floral structures, movements, and patterns of wettability. Microclimate influences the timing of flower-opening, anther extrusion and dehiscence, the survival and germination of pollen grains, and the exposure and receptivity of the style. Weather- related effects on pollinator activity operate indirectly through floral reward (the secretion rate and sugar concentration of nectar, and the release, texture, and perhaps digestibility of pollen) or directly through the hygrothermal balance of the insect or bird, to an extent that depends on the shape of the flower and the deg...

Pollination and the weather

Waterlogging usually results from overuse and/or poor management of irrigation water and is a serious constraint with damaging effects. The rapidly depleting oxygen from submerged root zone is sensed and plant adjusts expressing anaerobic proteins. Plant cells shift their metabolism towards low energy yielding anaerobic fermentation pathways in the absence of oxygen. Structural modifications are also induced as aerenchyma formation and adventitious rootings, etc. Studies at molecular and biochemical levels to facilitate early perception and subsequent responses have also been worked out to produce resistant transgenic plants. This review explores the sequential changes of plant responses at different levels regarding their defense strategies and efforts made to enhance them, tailoring crucial regulators so that they can withstand waterlogging stress.

Physiological and biochemical changes in plants under waterlogging

Callose provides a useful phenotypic bioassay in plant breeding to determine: incompatibility system; gametophytic competition; and stigma and ovule viability. Callose appearance in ovules may be associated with senescence, and used to determine the effective pollination period. In incompatible matings, callose formation is specific and related to rejection phenomena. The stigma callose response is induced by informational molecules carried by the germinal line, i.e. self or interspecific pollen, but not by the somatic line. Several methods of visualizing callose are reviewed. The role of callose in pollen-stigma interactions has many analogies with host-parasite interactions, and a model is proposed based on relationships between callose, boron and inhibitor (phytoalexin-like) synthesis. The callose response provides a useful tool for the biotechnology of seed production.

Callose and determination of pistil viability and incompatibility.

https://www.avocadosource.com/Journals/Elsevier/scientiahort_1985_25_99-110_Scholefield.pdf

Carbohydrate cycling in relation to shoot growth, floral initiation and development and yield in the avocado

https://www.avocadosource.com/Journals/Elsevier/scientiahort_1981_14_27-33_sedgley.pdf

Flowering and fruit-set response to temperature in the avocado cultivar 'hass'

https://www.avocadosource.com/Journals/Elsevier/scientiahort_1983_18_207-213_Sedgley.pdf

Effect of low temperatures during flowering on floral cycle and pollen tube growth in nine avocado cultivars

https://avocadosource.com/journals/elsevier/scientiahort_1977_7_27-36_sedgley.pdf

M. Sedgley

Papers

Carbohydrate cycling in relation to shoot growth, floral initiation and development and yield in the avocado

Flowering and fruit-set response to temperature in the avocado cultivar 'hass'

Effect of low temperatures during flowering on floral cycle and pollen tube growth in nine avocado cultivars

Reduced pollen tube growth and the presence of callose in the pistil of the male floral stage of the avocado

Pollen tube growth in macadamia