Calcium (Ca) oxalate crystals occur in many plant species and in most organs and tissues. They generally form within cells although extracellular crystals have been reported. The crystal cells or idioblasts display ultrastructural modifications which are related to crystal precipitation. Crystal formation is usually associated with membranes, chambers, or inclusions found within the cell vacuole(s). Tubules, modified plastids and enlarged nuclei also have been reported in crystal idioblasts. The Ca oxalate crystals consist of either the monohydrate whewellite form, or the dihydrate weddellite form. A number of techniques exist for the identification of calcium oxalate. X-ray diffraction, Raman microprobe analysis and infrared spectroscopy are the most accurate. Many plant crystals assumed to be Ca oxalate have never been positively identified as such. In some instances, crystals have been classified as whewellite or weddellite solely on the basis of their shape. Certain evidence indicates that crystal shape may be independent of hydration form of Ca oxalate and that the vacuole crystal chamber membranes may act to mold crystal shape; however, the actual mechanism controlling shape is unknown.

Calcium oxalate crystals in plants

Biochemistry and Physiology oj Plant Hormones is intended primarily as a textbook or major reference for a one-term intermediate-level or advanced course dealing with hormonal regulation of growth and development of seed plants for students majoring in biology, botany, and applied botany fields such as agronomy, forestry, and horticulture. Additionally, it should be useful to others who wish to become familiar with the topic in relation to their principal student or professional interests in related fields. It is assumed that readers will have a background in fundamental biology, plant physiology, and biochemistry. The dominant objective of Biochemistry and Physiology oj Plant Hor mones is to summarize, in a reasonably balanced and comprehensive way, the current state of our fundamental knowledge regarding the major kinds of hormones and the phytochrome pigment system. Written primarily for students rather than researchers, the book is purposely brief. Biochemical aspects have been given priority intentionally, somewhat at the expense of physiological considerations. There are extensive citations of the literature-both old and recent-but, it is hoped, not so much documentation as to make the book difficult to read. The specific choices of publications to cite and illustrations to present were made for different reasons, often to illustrate historical develop ment, sometimes to illustrate ideas that later proved invalid, occasionally to exemplify conflicting hypotheses, and most often to illustrate the current state of our knowledge about hormonal phenomena."

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Biochemistry and Physiology of Plant Hormones

The tissue of resting plant storage organs such as carrots, red beets, sugar beets or potato tubers can be activated by slicing into thin disks and incubation of these fragments in a moist atmosphere for different periods of time (“aging”). Activation comprises the turning-on of various genes with subsequent synthesis of transfer-, ribosomal and messenger RNAs and their transport into the cytoplasm. The immediate consequence of all these primary reactions is a vigorous synthesis of various enzymes and structural proteins which enable the cell to greatly enhanced metabolic activities. Thus, degradation of storage polymers and the procession of the resulting products through glycolysis, the pentose phosphate shunt and the shikimateprephenate-pathway and cellulose biosynthesis occur. Deinhibition of the tricarboxylic acid cycle opens the flow of metabolites into fatty acid, phospholipid and steroid biosynthesis, simultaneously providing the respiratory chain with electrons. In spite of functional modifications within the electron transport chain, the enhanced respiration of tissue slices serves as an energy source for the various energy-dependent reactions of the cell such as syntheses and the uptake of solutes. All of these activities accompany a concomitant dedifferentiation process and ultimately lead to renewed redifferentiation of the tissue slice cell.

Metabolism in plant storage tissue slices

The naturally occurring auxin, indole‐3‐acetic acid, is thought to regulate normal growth and developmental processes in higher plants, including cell extension, cell division, and cell differentiation. Applied auxins, including synthetic and natural auxins, can dramatically alter normal growth and developmental patterns, and applied auxins have been shown to modify expression of genes transcribed by all three classes of nuclear RNA polymerase (i.e., RNA polymerase I, II, and III). The regulation of specific genes by auxin may occur over long (e.g., several hours to days) or short (e.g., minutes) time spans after hormone application. The more interesting responses to applied auxins are the short‐term responses since these are more likely primary responses to the hormone. Several experimental approaches have been used to demonstrate that applied auxins rapidly alter gene expression, and these include in vivo labeling of polypeptides, in vitro translation of mRNAs, and cDNA cloning of auxin‐regulated mRNAs ...

Auxin‐regulated gene expression in higher plants

INTRODUCTION ...... . . . ...... ..... .... .. ......... .. .. ........ . 538 HORMONAL MODIFICATION OF RNA METABOLISM . 538 Auxin 538 Receptors and mediators 538 Regulation of transcription (isolated nuclei, chromatin, and DNA) 540 Polymerases ....... ... ...... ... .... 542 Regulation of RNA metabolism in vivo ......... 543 Gibberellins .. ..... ....... ..... ......... .. .. ... 545 Receptors 545 Regulation of transcription (isolated nuclei, chromatin, and DNA) 545 Regulation of RNA metabolism in vivo 546 Cytokinins . ..... ... 549 Receptors ... ..... ... 549

Regulation of Ribonucleic Acid Metabolism by Plant Hormones

Gibberellic acid breaks dormancy of hazel seeds. Markedly preceding growth of the embryonic axis is an increased RNA synthesis, as shown by total RNA determination and 32P incorporation into RNA. This increased RNA synthesis is accounted for by an increase in DNA template available for transcription and (subsequently) increased RNA polymerase activity. It is suggested that gibberellic acid breaks dormancy by a mechanism of gene derepression, as indicated by increased chromatin-directed RNA synthesis as measured in vitro.

Increased nucleic-acid synthesis in relation to the breaking of dormancy of hazel seed by gibberellic acid.

Enhancement by 2,4-dichlorophenoxyacetic acid of chromatin RNA polymerase in soybean hypocotyl tissue.

Dormanit seeds of Hazel (Cworylus avellatta L.) re(luire a period of after-ripeniing at low temliperlat'ire before they beconme capable of subsequent germiination. (Gibberellic acid (GA;) c-n fully replace this requirement (2, 6). The identification of gibberellin-likz substar.s in extracts of chilled ( noni-dormant) seeds led Frankland and Wareiing (7) to suggest that gibberellin synthesis nmay be involved in the after-ripening process. GA, lhas also beeni sho -n to iniduce synthesis of hlydrolytic enzymiles in other seed tissues (13) and enhlanice RNA svynthesis in isolated nluclei of pea seedlings (9). Since derepression of genetic material has beeln shown to accompany the breaking of l)otato bud dormiiancy by ethylene chlorohydriii ('12) the possibility arises that the breaking of dormancy bv GA, ma similarly r .,ult in gene derepression. To test this possibility we have studied the effect of GA3 on chromatin-directed RNA synthesis in relation to the breaking of Hazel seed dormancy. All seeds were sterilized for 5 min in 0.5 % sodium hypochlorite, sowl1 on absorbant paper soaked witt. water or GiA;, '(1 ug/nil) and subsequently maintained at 25° in the dark for the required period. Embryonic axes were then excised by severing the cotyledonary ipetioles. KINA synthesis was measured y)V ,2O9 incorporation. Twenty embryonic axes were incubate(l f(r 3 hr in 1 nil of me(liutm (125 ,Lc ''1(4'1 % Sucrose an(l an() n\1 amonium acetate b)uffer, pH 6.0) at 250 and nucleic acids subsequently extr acte(l by the l)llenol-dupanol miethio(d of Cherry ct ild. (5). Polyacrylamnide gel electrophoresis was used to fractionate the RMTA specie:, (based on 1). alt'.:ough the data presented here represents total RNA. Gel electrophoresis also establislhed, on thle l)asis of molecular weight, that there was no significant incorporatiotn of label into bacterial RNA in any samples (unipublished data). Chromatin was prepared from emibryonic axes by general methods based on those of Huang and Bonner (8) and

Increased DNA template and RNA polymerase associated with the breaking of seed dormancy.

The germination of lettuce seeds is inhibited by the nucleotide base analogue 6-methylpurine. RNA synthesis has been measured during imbibition and germination as (32)P-phosphate incorporation into RNA species as fractionated by polyacrylamide gel electrophoresis. Seeds were surface sterilized and imbibed in the presence of various antibiotics. RNA preparations from lettuce seeds were coelectrophoresed with (3)H-RNA prepared from bacteria to check for bacterial contamination of the seeds. There is a much higher rate of RNA synthesis in illuminated, germinating seeds as compared to dark, non-germinating seeds. This difference does not develop until after 12 hours of imbibition at 27°, which is the time of onset of germination and radicle growth.

RNA synthesis and the germination of light-sensitive lettuce seeds.

Chromatin-associated RNA polymerase activity increases during washing of sugar beet tissue to a maximum by 20 hours. This increase was inhibited by dosages of gamma irradiation between 50 and 400 krad. Template availability, as measured by saturating levels of added Escherichia coli RNA polymerase, also increased with washing and was inhibited, although to a lesser extent, by the above irradiation dosages. Neither endogenous polymerase activity nor template availability was affected by high dosages (300 krad) in unwashed tissue. Exposure of tissue to irradiation (300 krad) at different times during a 20-hour washing period severely inhibited the development of RNA polymerase activity during the early stages of washing. The inhibition of template availability, however, was independent of time of irradiation. The data presented are discussed in relation to the mechanisms involved in the inhibitory effects of gamma irradiation on RNA production and subsequent protein synthesis.

B. C. Jarvis

Papers

Increased nucleic-acid synthesis in relation to the breaking of dormancy of hazel seed by gibberellic acid.

Enhancement by 2,4-dichlorophenoxyacetic acid of chromatin RNA polymerase in soybean hypocotyl tissue.

Increased DNA template and RNA polymerase associated with the breaking of seed dormancy.

RNA synthesis and the germination of light-sensitive lettuce seeds.

Effects of gamma irradiation on chromatin activity of sugar beet tissue.