Effects of the fungal toxin, tentotoxin, on development and chlorophyll accumulation of plastids of primary leaves of mung bean [Vigna radiata (L.) Wilczek cv. Berken] were studied using spectrophotometric, electrophoretic, and microscopic procedures. In etioplasts of control tissues both prolamellar bodies and prothylakoids occurred, whereas small vesicles were associated with structurally distinct prolamellar bodies in tentoxin‐affected etioplasts. As determined by in vivo spectrophotometry, tentoxin‐affected etioplasts had 25% less phototransformable protochlorophyll(ide) and 35% less non‐phototransformable protochlorophyll(ide) than had control etioplasts after 5 days of dark seedling growth. Tentoxin had no effect on the rate of the Shibita shift. Protochlorophyll(ide) resynthesis in the dark immediately after protochlorophyll(ide) phototransformation was five to six times slower in tentoxintreated than in control tissues. Effects on chlorophyll(ide) content were observed within 30 min of the beginning of continuous white light exposure. In vivo measurement of cytochrome f redox activity revealed that this cytochrome was linked to light‐driven electron flow in control tissues within 20 min of the beginning of continuous white light, whereas in the tentoxin‐treated tissues there was no linkage (despite the presence of cytochromef) at any time. Coupling factor 1 was present and had potential ATPase activity in both control and tentoxin‐affected plastids. There was about sixteen times more chlorophyll in control than in tentoxin‐treated tissues in continuous as well as in intermittent (2 min light/118 min dark) light. These data are consistent with the view that tentoxin disrupts normal etioplast and chloroplast development through a mechanism unrelated to photophosphorylation.

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The active, far‐red light absorbing, form of phytochrome was found to inhibit growth and phytochrome levels in the mesocotyl and coleoptile of 4‐ to 5.5‐day‐old seedlings of Zea mays L. Short, low‐irradiance red or far‐red light treatments were used to produce different proportions of active phytochrome at the end of highdirradiance white‐light periods, which left different levels of total phytochrome in the plants. After light treatments which left relatively high levels of spectrophotometrically assayable phytochrome in the seedlings, apparent phytochrome synthesis in the subsequent dark period was low regardless of the proportions of each form of the pigment present at the beginning of the dark period. In light treatments producing relatively low levels of assayable phytochrome, levels of apparent phytochrome synthesis in both red and far‐red treatments and differences between apparent synthesis in red and far‐red treatments were maximal. No simple correlation was found between growth and apparent phytochrome synthesis. However, growth and total phytochrome levels were positively correlated in both organs. Using a subtractive method of correlation, in which only phytochrome effects were plotted, strong linear relationships between phytochrome levels or longitudinal growth and Pfr levels were found in those light treatments leaving greater than 8% of dark control levels of phytochrome in the tissues. Using this technique non‐linear, inverse relationships between Pfr and apparent phytochrome synthesis was found, indicating that modes of phytochrome control over phytochrome synthesis and growth differ. Our results are consistent with the view that in vivo assays of “bulk’ phytochrome reflect levels and states of the physiologically active phytochrome fraction under our experimental conditions in maize.

The effects of 20 \iM tentoxin on mesophyll chloroplast ultrastructural development, chlorophyll organization and accumulation, and pigment transformations in cotyledons of dark-grown, 4-day-old ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea] were monitored. After 6 h of white light (200 |xE m~^ s~'), many plastids of tentoxin-treated tissues contained prolamellar bodies or inconsistent internal membrane orientation in contrast to the uniform internal membrane orientation and absence of prolamellar bodies in controls. Grana stacking did not progress beyond three to four disc loculi in tentoxin-treatments, and fret membranes were usually discontinuous and reduced. Cylindrical or cupped grana appeared in many chloroplasts after 3 days of light, while other chloroplasts in which disruption was more pronounced had few grana except for remnants, but usually did possess vesicles or structures resembling prolamellar bodies. Tentoxin had no apparent effect on stroma density or plastoglobuli size and number. No starch grains appeared in any of the tentoxin treatments, whereas they appeared after 24 h in controls. Initial protochlorophyllide content and its photoconversion to chlorophyllide and subsequent Shibata shift were not affected by tentoxin. Chlorophyll accumulation rates in tentoxin-treated cotyledons were about 10% of control rates during the first 24 h of greening and about 20% of controls from 48 to 72 h of greening. Chlorophyll a/b ratio and PSU size (total Chl/P700) were not significantly affected by tentoxin.

Abstract. Brief, low energy (approximately 400 Kerg cm-2) red light interruption of the early dark-growth period of Zea mays L. cv