Intact Pea Seedlings Research Articles

Some Effects of 1-Amino-2-Nitrocyclopentane-1-Carboxylic Acid on Flowering Plants

A study has been made of the effects on higher plants of i-amino-2-nitrocyclo-pentane-1-carboxylic acid (ANPCA), a metabolite of Aspergillus wentii Wehmer. ANPCA was rapidly translocated to young tissues when injected into the stems of pea seedlings, but when applied to the roots of very young seedlings only trace amounts entered the plants. In intact plants ANPCA produced loss of apical dominance and shorter internodes but was without effect on isolated stem or leaf sections. There was some reduction of cell extension in the internodes of intact pea seedlings, but the main effect was on cell numbers. ANPCA inhibited mitosis in root tips and apical buds, the degree of inhibition varying with the species. There appeared to be a block in the mitotic cycle between the end of DNA synthesis and prophase. Inhibition caused by ANPCA could be reversed by L-leucine. Chlorophyll synthesis was inhibited by ANPCA in newly formed tissue and in etiolated leaves transferred to the light. There was a considerable increase in the free amino-acid pool and a decrease in gibberellin content due to treatment with ANPCA. It is suggested that the primary effect of ANPCA may be on protein or RNA synthesis.

The Stimulation by Gibberellic Acid of Cell Wall Synthesis in the Dwarf Pea Plant

Gibberellic acid (GA) brought about an increase in the rate of dry-weight incorporation into expanding internodea of intact dwarf pea seedlings. The amount of water present in expanding internodes was closely correlated with internode dry weight, and the slope of the relation was unaffected by GA treatment. It is proposed that the effect of GA upon internode expansion is mediated through the change in dry weight. Part of the increase in dry weight brought about by GA was attributable to an increase in the weight of cell wall material. The amount of water present in expanding internodes was found to be correlated with the amount of wall material present. It is possible that the increased rate of wall synthesis which follows GA treatment allows an increase in the rate of cell expansion.

The effect of high concentrations of heavy water on root development inPisum sativum andZea mays

The early effects of D/sub 2/O (50 to 90%) on pea and corn seedlings were examined. When the roots of intact pea seedlings are immersed in high concentrations (80 to 90%) of D/sub 2/O for 24 hr, no increase in root length occurs. Immediately above the root apex, swellings occur as a result of widening of cortical cells and parenchymatous components of the stele, and disturbances of the vascular pattern are also observed. In roots which are grown out after treatment, no laterals are found along that portion corresponding to the region of elongation at time of treatment. Their development is blocked at the primordial level. Growth rates of roots after 24-hr treatment are proportionai to the D/sub 2/O concentrations applied. The mitotic index of pea roots approaches zero within eight hr after immersion in 70 to 90% D/sub 2/O. At concentrations lower than 90%, mitoses recommence while the roots are still in heavy water. The mitotic cycle appears to be partially phased as a result of the treatment. In corn roots, two mitotic blocks occur during the first hour of D/ sub 2/O exposure; the first prevents the flow of cells into prophase, the second occurs at the endmore » of metaphase. The preprophase block is released after 1/4 hr and the renewed flow of cells added to the cells held in metaphase increases the mitotic index above that of the controls. After the first hour of treatment a general suppression of mitotic activity sets in. In peas the mitotic index drops continuously and more rapidly than in corn. Both peas and corn can adapt to growth in 80% D/sub 2/O. Whereas all pea roots resume growth after the first 8 hr, those of corn require 48 hr before 1/3 of the population shows renewed mitotic activity. Thus, the monocot in most ways is much more sensitive to high concentrations of heavy water than the dicot. One exception may be in relation to anatomical changes brought about by this treatment, since peas showed much greater disturbances in vascularization. (BBB)« less