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Abstract: Spermidine prevented the loss of chlorophyll from detached komatsuna (Brassica campestris cv. komatsuna) leaves in the dark but caused a striking reduction in light. It also inhibited photochemical activity in leaves incubated in the dark and light. Striking changes were seen in the chloroplast ultrastructure in light; the envelope was lacking, grana were dilated and thylakoids were distributed throughout the cytoplasm.

Abstract: Cycloheximide retarded the loss of chlorophyll from detached komatsuna (Brassica campestris cv. Komatsuna) leaves during incubation in the dark but promoted its loss in light. Cycloheximide-induced chlorophyll bleaching in light was prevented by some active oxygen scavengers. Chloroplast envelopes of cycloheximide-treated leaves incubated in both the dark and light were destroyed within 48 h. The grana of cycloheximide-treated leaves incubated in light were dilated.

Pigment constitution of a photochemically active chromoprotein (ACP) isolated from the blue-green alga Anabaena cylindrica, was immunologically studied. Results confirmed our previous view that ACP is a complex of c-phycocyanin and a pigment having absorption peaks at 480 and 695 nm. Antisera of both ACP and phycocyanin did not significantly affect the photochemical activity of ACP.

In-vivo phytochrome determinations in totally etiolated rice seedlings with a dual-wavelength spectrophotometer showed that on a fresh weight basis phytochrome concentration was highest in the coleoptile apex (0.175 of mean) ?(? O.D.) g-1 (fresh weight). The age of the seedlings had little effect on the pattern of phytochrome distribution in the coleoptiles.

The mechanical properties of the cell wall were measured in coleoptiles of totally etiolated rice seedlings. Coleoptiles were either decapitated or briefly exposed to red (R) and/or far-red (FR) light. The elastic and plastic extensibilities of the cell wall changed with age (length) of the coleoptiles. Decapitation and exposure to R induced changes in these properties, and the time-courses were similar. Following decapitation or R irradiation, the plastic extensibility of the cell wall decreased more conspicuously than elastic extensibility. Exogenous application of auxin immediately following decapitation alleviated the effect of removal of the tip. FR irradiation reduced both kinds of extensibilities, but its effect was much less than that of R, and it reversed the R-induced effect to the level of tissue treated with FR only. In repeated R-FR treatments, the decrease of elastic extensibility by R and its reversal by FR could be repeated, but the effect of a second irradiation with R after FR on plastic extensibility was not as apparent as that of the first. Reduction of cell-wall extensibility of etiolated rice coleoptiles caused by R light appeared, at least partly, to be due to a reduced auxin supply in the elongating region from the tip, similar to that caused by decapitation.

Temperature-dependent inhibitive actions of α,α′-dipyridyl and cycloheximide on the senescence of maize leaves were studied. α,α′-Dipyridyl effectively inhibited the loss of chlorophyll at 25�C but not at 35�C. Gycloheximide was highly effective in preserving chlorophyll at both of 25 and 35�C. Spectral analysis of senescent leaves at 35�C in α,α′-dipyridyl showed simultaneous bleaching the carotenoid and chlorophyll.

Coleoptile growth of intact rice seedlings under submerged conditions was not much affected by the continuous irradiation of red light. But, if aerated, growth was strongly inhibited by a low-energy brief irradiation of red light, and this red light-induced effect was reversed by a brief exposure to far-red light. The responses to red and far-red light were repeatedly reversible. The amount of photometrically detectable phytochrome in non-aerated coleoptile tissues was found to be as low as one third that in aerated ones. After the conversion of Pr to Pfr by a brief red irradiation, the total Δ (ΔA) of the aerated tissues decreased to about one fifth that of the original level within 6 hr at 24�C, while the Pfr in the non-aerated tissues was significantly less decayed.

A photoreactive component, P690, was isolated from ACP by successive treatments with SDS and Triton X 100. The isolated P690 is a chromoprotein with a molecular weight of 50,000 daltons and an isoelectric point at pH 9.1. Its spectrum has absorption maxima at 275, 450, 475, 630 and 690 nm and it emits, at –196�C, a fluorescence at 695 nm. The photochemical oxidation-reduction reaction activity is fully retained in the P690. The isolated P690 forms a complex with phycocyanin in vitro. This complex was identical with the original ACP in all characteristics examined. The complex formation of P690 is specific to phycocyanin. A possible mechanism for ACP formation is discussed.

The relationship between a photochemically active chromoprotein (ACP) (cf. ref. 1) and photosystem II was investigated with membrane fragments of Anabaena cylindrica, A. variabilis and P. boryaman. ACP was solubilized from membrane fragments of A. cylindrica but not from those of A. variabilis or P. boryanum, when the membrane fragments had been incubated in a dilute buffer and had lost their Hill or photosystem II activity. In A. cylindrica, ACP-solubilization always occurred, independent of photosystem II inactivation, on incubation of the membrane fragments in media without PEG. However, the amount of ACP solubilization accompanying photosystem II inactivation was twice that without photosystem II inactivation. The increase in ACP solubilization accompanying photosystem II inactivation. The kinetics resembled those for the decrease in 695 nm fluorescence emitted by membrane fragments at — 196�C (cf. 2). The ACP solubilized independent of photosystem II inactivation was assumed to have been released during disruption of intact cells in the preparation of membrane fragments. The slow ACP solubilization upon the inactivation of photosystem II was attributed to the pigment being bound to membranes. We assume that the photo-reactive component of ACP, P690 (cf. 3, 4), is released from the membranes during photosystem II inactivation, and that P690 is a component of photosystem II which emits the 695 nm fluorescence at — 196�C.

The senescence of maize and hydrangea leaves after being detached and kept in the dark was studied in terms of the loss of chlorophyll. Chlorophyll was more rapidly degraded in maize than hydrangea during the incubation period in the dark. The loss of chlorophyll in the dark was effectively inhibited in both plants by α,α′-dipyridyl and o-phenanthroline at concentrations between 0.01 and 0.1 mM. Three other chelators of iron produced lesser inhibition and only at higher concentrations. EDTA prevented the loss of chlorophyll in maize leaves at concentrations above 10 mM, but did not do so in hydrangea leaves. Detached leaves floated on EDTA, α,α′-dipyridyl or o-phenanthroline solutions and exposed to light exhibited a marked bleaching. The bleaching was partially inhibited by applying ascorbic acid.

The senescence of maize and hydrangea leaves after detachment and darkening was studied in terms of the loss of chlorophyll and protein. Chlorophyll contents of the detached leaves decreased in the dark in both plants. Cycloheximide at 0.1 mM effectively inhibited the loss of chlorophyll in maize, but did not do so in hydrangea. Continuous irradiation with white light of 4.6 Wm−2 prevented the loss of chlorophyll in hydrangea leaves, while it caused bleaching of maize leaves. Reducing agents such as ascorbic acid and glutathione did not prevent the bleaching by light. In maize leaves, the amount of protein decreased in the dark more slowly than that of chlorophyll, and cycloheximide slightly prevented the protein decrease. Continuous light irradiation of 4.6 Wm−2 delayed the loss of protein more effectively than cycloheximide did.

Photochemical, spectroscopic and fluorescence characteristics of the active chromo-protein (ACP) of Anabaena cylindrica were studied with preparations having different spectroscopic characteristics. Purified ACP preparations occasionally showed spectroscopic characteristics differing considerably from those of ordinary ACP. A spectroscopic difference in these preparations was observed only in the relative absorbance in the 620 nm peak. Absorption peaks at 430, 460, 480 and 695 nm remained unchanged. Photochemical activity and fluorescence yield at 700 nm were fairly constant in these preparations, when excited at absorption bands other than 620 nm. Spectroscopic changes caused by heat and detergent (SDS) treatments occurred only in the relative absorbance of the 620 nm peak. Photochemical and fluorescence characteristics of the treated ACP were the same as those of the ACP originally having a different absorption spectrum. A comparison of various ACP preparations indicates that ACP is a complex of two pigments, c-phycocyanin and a pigment with a 695 nm absorption maximum. The reduction in the molecular size of ACP by SDS-treatment indicates that pigment 695 is far smaller in its molecular size than c-phycocyanin. A possible function of the two pigments in the photochemical reaction is also discussed.

Pigment constitution of a photochemically active chromoprotein (ACP) isolated from the blue-green alga Anabaena cylindrica, was immunologically studied. Results confirmed our previous view that ACP is a complex of c-phycocyanin and a pigment having absorption peaks at 480 and 695 nm. Antisera of both ACP and phycocyanin did not significantly affect the photochemical activity of ACP.

Elongation growth induced by exogenous auxin of apical coleoptile segments of etiolated rice seedlings was promoted by ethylene. In the absence of exogenous auxin, growth promotion was not observed. The highest promotion by ethylene was obtained at 10−6 M of indole-3-acetic acid, a suboptimal concentration for auxin-induced elongation. Level of ethylene which achieved the effect was less than 1 µl per liter of an incubation atmosphere.