Growth Substances in the Roots of Vicia faba II. THE EFFECTS OF AGEING AND EXCISION OF THE MAIN TAP-ROOT MERISTEM

A quantitative chromatographic study has been made of the changesin the activity and distribution of the main ether-soluble acidauxins of Vicia faba seedling root systems during developmentand resulting from excision of the main tap-root meristem. AnIAA-like auxin (AP (ii)) is apparently synthesized predominantlyin apical and at a lower rate in lateral meristems. Productionseems to stop when meristematic growth stops. Its concentrationin mature extended cells is much lower and may fall to zeroin old cells, suggesting active degradation by an auxin-oxidase.Excision of the main tap-root tip gradually results in a greatlyaugmented production of AP (ii) in lateral meristems, conceivablythe result of correlative growth promotion. A second auxin and root-growth inhibitor (AP (iii)) is presentat higher activity levels than AP (ii) in tap-root meristemsand at the same level in lateral meristems. In mature cellsits activity is much lower than that of AP (ii). In contrastto AP (ii) it accumulates in both tap-root meristems and maturetissue as the root system ages. It could also be produced duringmeristematic growth but is not subsequently degraded. As withAP (ii), excision of the tap-root tip brings about a great increasein its concentration in lateral tips. A third auxin and root-growth accelerator (AP (i)) (accelerator?) is present in lower concentrations in both meristem and maturetissue. Its concentration tends to decrease with ageing and,in lateral meristems, is not affected by tap-root tip excision. It is suggested that AP (ii) produced by the meristem is normallyat suboptimal levels in the extending cells and may be the principalhormone controlling extension growth. AP (iii) accumulationmay account for growth deceleration on ageing. The role of AP(i) remains obscure. It is unlikely that correlative effectsof the taproot tip on lateral root growth are exercised directlyvia these auxins.     

Studies on the Geotropism of Roots: III. EFFECTS OF GEOTROPIC STIMULATION ON GROWTH-SUBSTANCE CONCENTRATIONS IN VICIA FABA ROOT TIPS

The auxins contained in 5-mm. tips of horizontal Vicia fabaroots have been compared with those in tips of vertical rootsafter cold ethanol extraction, paper-chromatographic separation,and Avena mesocotyl bioassay. At about the time curvature commencesin horizontal roots there is a marked increase in the contentof an auxin corresponding to ‘AP(ii)’ of pea roots(Rf 0.35–0.65 in isobutanol/methanol/water). There areindications that this is not due to its release from an inactivebound state but that it is either synthesized de novo or maybe converted from another auxin corresponding to ‘AP(iii)’of pea roots (Rf 0.75–1.0). The literature dealing with the auxins of geotropically stimulatedorgans is reassessed and it is concluded that, with the exceptionof the Avena coleoptile, there is very little evidence favouringa simple transport redistribution of auxin under gravity; themajority of the data favour an effect of gravity on auxin metabolism.     

Performance and Metabolic Alterations in Sesamum indicum L. under Different Intensities of Water Stress

Effects of mild (     

Salinity-induced enhancement of L-myo-inositol 1-phosphate synthase in rice (Oryza sativa L.)

The salt-tolerant varieties of rice (Oryza sativa L.) exhibit enhanced activity of the chloroplast form of L-myo-inositol 1-phosphate synthase (EC 5.5.4.1) under NaCl treatment either during the seedling stage or in fully grown plants during field growth. The salt-induced enhancement was noticeable only in chloroplasts from light-grown plants. The effects of these treatments on the cytosolic inositol synthase activity were less pronounced. While the effect of salt on the activity of the two forms was marginal in the salt-sensitive varieties during seedling growth, salinity affected the chloroplast inositol synthase activity adversely in these varieties during growth of the plants under field conditions. The salt-enhanced activities of inositol synthase(s) in the highly salt-tolerant varieties studied were found to be comparable to that observed in Porteresia coarctata, a halophytic wild rice species. The implications of these findings, which suggest a role of the inositol pathway in osmoregulation, are discussed.     

Growth Substances in the Roots of Vicia faba

An investigation has been made into the growth regulators presentin ethanol extracts of the seedling roots of Vicia faba afterseparation on paper partition chromatograms, using segmentsof Avena coleoptiles and mesocotyls and of Pisum sativum.rootsas biological assay material. Acetonitrile purification shows the presence of at least threeauxins running in isobutanol: methanol: water, at Rfs of 0–0·25,0·4–0·6, and 0·65–0·95;the latter may represent two different auxins. A similar, butclearer, picture is shown by the ether-soluble acid fraction.Here an auxin at Rf 0–0·25 also stimulates rootgrowth and could be ‘accelerator ’. A second atRf 0–0·25 is an indole compound which inhibitsroot growth and does not seem to be be IAA. A third at Rf 0·8–1·0is also a root-growth inhibitor and gives no indole reaction.The ‘inhibitor ß’ complex was demonstrated(Rf 0·65–0·85) together with a number ofother inhibitors at lower Rf value. The ether-soluble neutral component also contains auxins orauxin precursors. The water-soluble, ether-insoluble fraction contains four readilyinterconvertible substances with auxin properties. They allappear to inhibit root growth and give no indole reaction.