PLASTID DEVELOPMENT IN PRIMARY LEAVES OF PHASEOLUS VULGARIS

Abstract

Summary By the use of light and electron microscopy a quantitative investigation has been made of plastid membrane formation in the primary leaves of bean plants, during germination and growth in the dark. From 4 to 14 days of dark growth there was an eleven‐fold increase in cell number and a twenty‐six‐fold increase in plastid number per leaf. Formation of plastid envelope membrane between 6 and 14 days of dark growth amounted to 98 cm2 of membrane per leaf while the corresponding formation of internal plastid membrane was 272 cm2 per leaf. This internal plastid membrane appears to be formed, at least during the early stages of leaf growth, by the invagination of the inner envelope membrane. When a substantial amount of the thylakoid membrane has accumulated in the plastid a condensation process takes place to give the pro‐lamellar body, which is a structure composed of branching membrane tubules. Calculations based on the dimensions of these tubules have established that 1 μ3 of prolamellar body contains about 44 μ2 of membrane. Dark‐grown leaves have been found to contain all of the enzymes of the photosynthetic carbon cycle. The course of development, during dark growth, has been determined for the activities of eight enzymes of the photosynthetic carbon cycle and for two enzymes of the cytoplasm.

CHLOROPLAST DEVELOPMENT IN PRIMARY LEAVES OF PHASEOLUS VULGARIS

“…The pattern of etioplast development is similar to that already recorded (Berger and Feierabcnd, 1967;Bradbeer et al, 1974). Between day 3 and day 5 there is a noticeable lag period in the increase in plastid length when plants are exposed to the light by comparison with plants grown in the dark.…”

Etioplast Development in Dark-grown Leaves of Zea mays L.

“…If the interpretations of these profile shapes are correct this implies two phases of division in dark-grown maize leaves, each with its own division mechanism. Two phases of plastid division were also noted in etiolated primary leaves of bean by Bradbeer et al (4), one between days 4 and 7 and the other between days 9 and 12 of growth. The mechanism of the first division was not apparent while the second was thought to occur by plastid constriction.…”

“…The results of Robertson and Laetsch (20) who were able to show an increase in plastids/cell along etiolated barley leaves (ie. with age) and Bradbeer et al (4) who were able to show an increase in the total number of plastids in primary leaves of etiolated P. vulgaris L. of increasing age, confound this view. Dumbbell-shaped plastid profiles and plastid profiles with a central baffle at right angles to the long axis of the plastid have both been interpreted as division profiles (5).…”

“…There are also several interesting comparisons to be made between the observations reported here and those that have been made on etioplast development in the primary leaves of darkgrown Phaseolus vulgaris L. Despite discrepancies on the actual timing of the appearance of the PLB in this species (after 3 days, Weier and Brown [27]; after 9 days, Bradbeer et al 14]), points of similarity between the development in the two species are: the formation ofamyloplasts (4,(27)(28)(29), the subsequent disappearance of starch with the seemingly parallel increase in membrane, the rounded appearance of the plastid profiles, and the rapid increase in the size of both the plastid and the PLB at a precise stage in the EVELOPMENT 503 developmental sequence. Differences between the systems include a lack of association of ER with the etioplasts in maize (Whatley [29] also noted that this association was not as evident in maize as it was in bean) and the apparent absence of invaginations of the inner envelope membrane in maize.…”

“…Differences between the systems include a lack of association of ER with the etioplasts in maize (Whatley [29] also noted that this association was not as evident in maize as it was in bean) and the apparent absence of invaginations of the inner envelope membrane in maize. In bean it was thought that the internal lamellae were derived from these invaginations (4,27). A further difference appears to be one of the time scale of the development, in maize the time difference between defined developmental stages is in hours whereas in bean it can be in days.…”