Showing papers in "Annual Review of Plant Biology in 1968"

Ultrastructure and Physiology of Pollen

Abstract: Pollen offers opportunities and challenges because it is unique among higher plant "tissues." Yet this very uniqueness also adds to its value in research on fundamental and universal problems. Some of the special attrib­ utes which pollen presents to the investigator are discussed in this section of the review. Pollen is haploid, thereby providing genetically "simple" material. It grows singly in culture, behaving like .a unicellular organism, unconfined by neighboring cells. (In this paper pollen growth will refer, unless otherwise stated, to elongation of the pollen tube.) It can be cultured in vitro on sim­ ple, defined media, thereby permitting a fully controlled chemical environ­ ment. Yet the growth of pollen tubes in vitro seldom equals that in vivo, indicating that much remains to be learned regarding the nutritional and physical requirements for development of the pollen tube. Pollen grows rapidly. Pollen tubes are perhaps the most rapidly grow­ ing "cells" in the plant world, often achieving rates of several mm per hr in vitro. This means that pollen can, for many experimental purposes, be han­ dled like bacteria or other microorganisms, with many of the attendant ad­ vantages which these forms offer for research. While sterile pollen cultures are perhaps not necessary for short term experiments, they are available (103), and the way is thus open for handling pollen like microorganisms for a variety of metabolic and other studies. Similarly, techniques have been de­ scribed which largely eliminate the drawbacks which the small size of pol­ len fot:merly presented for certain types of biochemical, biophysical, and cy­ tochemical studies (51 ) . Pollen grows in a highly polar fashion, with

Salt Absorption by Plants

Abstract: Ion movement into and through plant cells has been a topic for many review articles in recent years (13, 14, 22, 28, 33, 48, 84, 86-88,99). Var­ ious facets of the total process have been examined in detail with varying degrees of success in relating one to the other. A review of the salt uptake process under such conditions may become a matter of consensus rather than development of irrefutable relationships. A plant or its organelles having a certain ion composition results from the sequential interactions between the plant and its ionic environment. The unknown presence of ions and molecules, or an improper evaluation of them in a system, can readily lead to divergent viewpoints on ion uptake. This suggests that the entry and accumulation of a single ion must necessarily involve interaction of other ions which ordinarily are neither considered nor accounted for in the uptake process. Thus, the more recent studies and those in the planning stage are being directed toward a multi-salt rather than a single-salt system.

Occurrence in Plants of Amino Acid Residues Chemically Bound Other-wise than in Proteins

Abstract: Almost ten years ago I summarized what was known about the chemi­ cally bound amino acids found in nonprotein substances in plants (241) and emphasized the fragmentary nature of our knowledge. Few chemically characterized substances had been found, and there were technical difficul­ ties in determining how much of compounds in this class might be present in aggregate in a given plant material. The present review is intended as a sequel to those remarks and as a survey of the literature not covered by previous reviews (24, 30, 36, 240, 242) and noticed in Chemical Abstracts up to the end of 1966. This literature is scattered and, despite help, here grate­ fully acknowledged, from colleagues in diverse fields, I must have missed significant contributions, and will be happy to be told of such, past and fu­ ture. This discussion deals first with technical aspects of determining such compounds and establishing that they are not artefacts and second with the chemical nature and biological activities of the compounds, together with such as is known of their metabolic relationships in the plant. Only algae (other than blue-green) and higher plants are considered. Recently Waley (261) has reviewed the naturally occurring peptides. This enables me to concentrate attention here on the compounds in this class that are not peptides. The boundary between 'proteins' and 'polypep­ tides' is as arbitrary as ever; I have continued to draw it in the region of mol wt 10,000. No attempt has been made to deal with pantothenic acid and related compounds. The conclusion emerges that many and varied substances belonging to this general class have been found in plants during the period under review. Few of these are simple a-linked oligopeptides. Many of them have impor­ tant physiological effects in plants or in other organisms, and have been found in the course of searches for such biologically active factors. Amino acids are synthesized by the plant as a first step in the course of protein biosynthesis; they also serve as points of departure for the biosynthesis of other, chemically very varied, end products. It need not therefore be sur­ prising to find that amino acid residues also occur, covalently bound, in a wide variety of nonprotein substances.