Response of Pea Stem Sections to Indoleacetic Acid, Gibberellic Acid, and Sucrose as Affected by Length and Distance from Apex

Effects of Gibberellic Acid and Sucrose on the Growth of Oat (Avena) Stem Segments

“…The GA-promoted growth in these segments was found to be primarily due to an increase in rate of cell elongation (18). Since gibberellins generally promote the growth of intact plant stems much more markedly than the growth of excised plant stems (5,25,29), the exceptionally large response and specificity to gibberellins observed in excised Avena stem segments presents a unique opportunity to study the mechanism of gibberellin-stimulated stem growth.An earlier attempt to correlate the gibberellin-promoted growth with the gibberellin-stimulated invertase activity indicated that the GA-enhanced invertase activity does not account for all of the gibberellin promoted growth in the segments (21). We are, thus, far from understanding the primary mode of action of gibberellins in growth stimulation of Avena segments.…”

Xi. Addendum

“…This was the case in Kato's experiments. This point of view is strongly supported by the work of Purves & Hillman (1958). Using sections cut from dark-grown pea stems taken at various distances from the apex, they found that sections nearer to the apex had a higher endogenous growth rate than those more distant; sections from the near-apical region showed the greatest response to GA, those more distant from the apex the greatest response to IAA.…”

“…However, while the effects of red light can be reversed by a subsequent exposure to far-red, the effects of G-4 are not so reversed, or at most only partially (Poljakoff-Mayber, . Further work on Lemna has been reported by Hillman ( 1957), confirming that the non-photosynthetic light requirement of this plant, though it can be replaced by kinetin, cannot be replaced by GX. More detailed accounts by Lockhart (1958a, 6 ) of the interaction between light and GA in their effects on stem extension of various dark-grown plants, confirms that in general light and GA have opposite effects and it may indeed be true that in a real sense GA specifically reverses the inhibiting effect of light in such cases.…”

“…Of particular interest is the observation that treatment of mature shoots of Hedera helix results in a reestablishment of the juvenile leaf-shape and habit of growth (Robbins, 1957); contrarily, in Ipomoea caerulea and Eucalyptus melliodora GA treatment induces more early development of adult forms of leaf shape (Njoku, 1958;Scurfield & Moore, 1958).…”

“…There has been a good deal of further work on dormancy-breaking effects of GA. Dormancy of potato tubers is broken systemically by foliar applications of GA; under such circumstances buds on the tubers have no rest period and, in consequence, the tubers become much branched and misshapen (Humphries, 1958b;Rappaport, Lippert & Timm, 1957 (1958) have demonstrated a marked synergism in mixtures of kinetin and GA in breaking lettuce-seed dormancy. Barley seed dormancy may also be broken partially or completely by GA; in some cases a marked synergism between GA and hydrogen sulphide has been found (Pollock, 1958).…”