This chapter is concerned with physiological factors that control levels of flavonoids accumulating in plants and with the biological implications of these accumulations both within the plant and in plant-animal (1ncluding man) interactions. Levels of flavonoids within plants are a reflection of the efficiency of biosynthesis (see Chapter 16) tempered by turnover and degradation (Chapter 17) during growth and development. These are all influenced by the external environment. The functions of flavonoids may be approached by a consideration of their general reactivity when introduced into biochemical systems, the many implications of their pigment characteristics, their possible mediation in plant growth and development, and their effects on animals and microorganisms.

https://link.springer.com/content/pdf/10.1007%2F978-1-4899-2909-9_18.pdf

Physiology and Functions of Flavonoids

Knowledge of the mature seed and its germination is of importance in the study of seed formation Indeed, embryogeny and germination are extensions of each other separated by a period of relative metabolic inactivity called quiescence, and are essentially different phases of the continuing process of embryo growth and development Obviously, the nature of the pre-quiescence embryo bears very heavily on early germination behaviour and its control, and answers to questions relating to germination behaviour are increasingly being sought during the period of seed development

The Seed: Germination

In a tuber which is in thermal equilibrium with its surroundings, metabolic heat production raises the temperature slightly above the environment — the specific heat of the tissue is about 3.6 J (g°C)−1 (Mann, reported in Burton, 1966) and a typical heat production of, say, 50 mJ g−1 h−1 (Section 14.1.4) could thus raise the temperature 0.014°C h−1 were it not transferred to the surrounding air. This transfer involves a temperature gradient of about 0.2°C from the centre to the periphery, and about 0.1°C from just below the skin to the surrounding air (Burton, 1969). These are the approximate equilibrium values.

The physics and physiology of storage

Polysaccharides such as starch, cellulose and other glucans, pectins, xylans, mannans, and fructans are present as major structural and storage materials in plants. These constituents may be degraded and modified by endogenous enzymes during plant growth and development. In plant pathogenesis by microorganisms, extracellular enzymes secreted by infected strains play a major role in plant tissue degradation and invasion of the host. Many of these polysaccharide-degrading enzymes are also produced by microorganisms widely used in industrial enzyme production. Most commerical enzyme preparations contain an array of secondary activities in addition to the one or two principal components which have standardized activities. In the processing of unpurified carbohydrate materials such as cereals, fruits, and tubers, these secondary enzyme activities offer major potential for improving process efficiency. Use of more defined combinations of industrial polysaccharases should allow final control of existing enzyme processes and should also lead to the development of novel enzymatic applications.

Enzymatic degradation of cell wall and related plant polysaccharides.

Summary. 
A review of the scientific literature relating to the physiology of potato (Solanum tuberosum) tuber dormancy is presented. Effort has been concentrated on an up-to-date overview of the current state of understanding, rather than comprehensively covering the very extensive literature going back over many decades. The format chosen follows the fate of the crop. After defining tuberisation and dormancy, the physiological activity of the dormant tuber is reviewed and the storage environment is considered from both a physical and chemical standpoint. Advances in chemical control and the potential for molecular biology are highlighted.

A review of the physiology of potato tuber dormancy.

The Role of Buds and Gibberellin in Dormancy and the Mobilization of Reserve Materials in Potato Tubers

Acid phosphatase activity was present in unimbibed barley seed, but rose during incubation of embryoless half-seeds and isolated aleurone layers, and was further increased by 10-6 M gibberellie acid (GA3). Release of total acid phosphatase activity from half-seeds and aleurone layers was markedly enhanced by GA3. Inhibitor studies with cycloheximide and actinomycin D suggested that de novo synthesis of acid phosphatase occurred following imbibition. Gel filtration, electrophoresis, and [14C]leucine incorporation studies revealed that a single molecu lar form of acid phosphatase was present in dry seed, whereas on incubation two further forms arose. A proportion of the three molecular forms of the enzyme was synthesized de novo. Gibberellie acid stimulated activation, but not de novo synthesis, of all three molecular forms of acid phosphatase. Although a small amount of one of the molecular forms was secreted in the absence of GA3, the presence of gibberellin greatly increased secretion of the same form of acid phosphatase.

Effects of Gibberellic Acid on the Activation, Synthesis, and Release of Acid Phosphatase in Barley Seed

Phaseolus multiflorus plants at three stages of development were decapitated either immediately below the apical bud or lower down at a point 1 cm above the insertion of the primary leaves. Growth regulators in lanolin were applied to the cut stem surface. IAA always inhibited axillary bud elongation and dry-matter accumulation, and enhanced internode dry weight but not elongation. GA3 applied below the apical bud greatly increased internode elongation and dry weight, but simultaneously reduced bud elongation and dry weight increase. Application of GA3 1 cm above the buds had no effect on bud elongation in the youngest plants, but enhanced their elongation in the two older groups. IAA always antagonized GA3-enhancement of internode extension growth, whereas its effects on GA3 enhanced dry-matter accumulation depended on the stage of internode development. Bud elongation was greater in plants treated with GA3 + IAA than in plants treated only with IAA, except in the youngest plants decapitated immediately below the apical bud, where GA3 caused a slight increase in IAA-induced bud inhibition. GA3 increased inhibition of bud dry weight by IAA in the two youngest groups of plants, but slightly reduced it in the oldest plants. No simple compensatory growth relationship existed between internode and buds. It was concluded that, (1) auxin appears to be the principal growth hormone concerned in correlative inhibition, and (2) availability of gibberellin to internode and buds is of importance as a modifying factor in auxin-regulated apical dominance by virtue of its local effects on growth in the internode and in the buds.

Factors Influencing the Distribution of Growth Between Stem and Axillary Buds in Decapitated Bean Plants

14C from indol-3yl-(acetic acid-2-14C) (IAA-14C) was transported in a weak but definitely polar manner through segments of young and matured regions of pea roots. Greater quantities of 14C-labelled material moved acropetally than basipetally. Up to 70 per cent of radioactivity originally present in donor agar blocks was taken up by the root segments, but only approxi mately 2 to 3 per cent of this emerged into the receiver agar blocks. Any differences in uptake, transport, or binding of auxin were very slight in the three regions of root studied. The IAA-14C was metabolized during passage through the root segments, yielding two principal radioactive products. The identities of these were not determined, but they appeared to have auxin activity and may be formed spontaneously, but more slowly, in solutions of IAA-14C. IAA-14C was transported into receiver blocks more readily than its radioactive derivatives. INTRODUCTION Basipetal polar transport of auxin in stems, hypocotyls, petioles, and coleoptiles of a range of plant species is now well established (Goldsmith, 1969). There has, however, been some considerable doubt until recently as to the pattern of auxin movement in roots. Studies of IAA-14C transport, using the agar-block method, have shown that polar auxin movement is acropetal in root segments from several species (Pilet, 1964; Kirk and Jacobs, 1968; Wilkins and Scott, 1968; Scott and Wilkins, 1968). On the other hand, some workers have found that in root segments of some species, auxin transport is so poor that no significant amounts of radio activity appeared in agar receiver blocks with either acropetal or basipetal transport. This was found to be the case for root segments of Convolvulus (Bonnett and Torrey, 1965), Vicia faba (Yeomans and Audus, 1964), and Pisum sativum (Wilkins and Scott, 1968). The experiments described below investigated the transport of 14C from IAA-2-14C in root segments of P. sativum cv. Alaska, using a relatively high auxin concentration and long transport periods. METHODS Segments 5 mm long were cut from seedling roots of 2-day-old dark-grown seedlings of P. sativum cv. Alaska. All handling of root segments, and transport tests, were carried out in dim green light and darkness. Cylinders of 1-5 per cent agar gel, 3 mm X 3 mm, were used 1 Present address: 15 Carlton Crescent, East Leake, nr. Loughborough, Leics., U.K. This content downloaded from 207.46.13.83 on Fri, 21 Oct 2016 04:45:08 UTC All use subject to http://about.jstor.org/terms 960 Hillman and Phillips—Transport of Indol-3yl-acetic Acid in Roots as donor and receiver blocks. Donor blocks contained 5-7 X 10~5 M IAA-2-14C (specific activity, 5-27 m Ci/mM). Segments and agar blocks were arranged for 14C-transport studies in the natural vertical position (apical end lowermost). Each segment, plus donor and receiver blocks, was placed on a separate aluminium planchet, covered with an inverted glass vial, and allowed to stand in darkness at 25±10C for varying periods of time. Five segments were used per treatment, and each treatment was duplicated. Each group of five agar receiver blocks was pooled for radioactivity measurement. Donor blocks were assayed individually, but counts obtained from five individual donors were totalled to correspond with the data obtained from receiver blocks. Agar blocks were trans ferred to 25-mm diameter aluminium plancheis and processed according to the method of McCready (1963). All receiver-block planchets were timed for 1000 counts, and donor blocks for 4000 counts. Standard, unused, donor blocks yielded a mean of 3470 cpm per block. Agar blocks were extracted by the freeze-extraction method of Jones and Phillips (1964) with five 2-ml aliquots of 80 per cent methanol. Root segments were coarsely ground and steeped in 2-ml aliquots of methanol for 24 h at 0 °C. Pooled methanolic extracts were con centrated under vacuum, and either loaded on Whatman No. 1 chromatography paper (development in isopropanol : ammonia (S.G. 0-88):water: : 10:1:1), or incorporated into a circle of Green's lens tissue for measurement of total counts. Chromatograms were divided into 10 equal transverse strips. Each strip was eluted with either 5 ml 80 per cent methanol (for radioassay), or with distilled water for bioassay. Methanol eluates were concentrated on lens tissue for radioactivity measurements. Bioassays were statistically analysed using the short-cut procedure of Tukey (1953). Standard deviations of radioactivity data were calculated.

Transport and Metabolism of Indol-3yl-(Acetic Acid-2-14C) in Pea Roots

Detailed time courses of germination were recorded for three seed batches of lettuce, cv. 'Great Lakes The germination of this variety is usually considered to be insensitive to light, but considerable variability was noted between seed batches with respect to the effect of light. Previous reports on the chemical induction of a light requirement for germination in lettuce seeds were not substantiated for this variety. Naringenin was found to be relatively ineffective, and although coumarin, ABA, and IAA all delayed germination with increasing concentration, this delay was not diminished by continuous light. The inhibitions of germina tion by sucrose, mannitol, Carbowax, sodium chloride, potassium chloride, and potassium nitrate were also similar in light and darkness ; these inhibitions appeared to relate to the osmotic pressures of the solutions. It is postulated that previous reports of chemical induction of a light requirement may be the result of presenting germination figures at one point in time. Analysis of germination by detailed time courses showed that while prolonged light irradiation slightly accelerated germination, perhaps by raising seed temperature, it in no way overcame chemical inhibition.

I. D. J. Phillips

Papers

The Role of Buds and Gibberellin in Dormancy and the Mobilization of Reserve Materials in Potato Tubers

Effects of Gibberellic Acid on the Activation, Synthesis, and Release of Acid Phosphatase in Barley Seed

Factors Influencing the Distribution of Growth Between Stem and Axillary Buds in Decapitated Bean Plants

Transport and Metabolism of Indol-3yl-(Acetic Acid-2-14C) in Pea Roots

Studies on the Chemical Induction of a Light Requirement for Germination in Seeds of Lettuce, Lactuca sativa L., cv. ‘Great Lakes’