Photosynthetic Studies on a Pea-mutant Deficient in Chlorophyll

Abstract

Abstract. A chlorophyll-deficient mutant of pea (Pisum sativum) was found as a spontaneous mutation of the variety Greenfeast. Total chlorophyll of the mutant leaves was about one-half that of normal pea leaves per mg dry weight, and the ratio of chl a:chl b ranged from 10 to 18, compared with 3 for normal pea. In each generation the mutant plants gave rise to normal and mutant plants and lethal plants with yellow leaves.For a normal pea plant, CO2 uptake was saturated at about 60,000 lux, whereas with mutant leaves, the rate of CO2 uptake was still increasing at 113,000 lux. At 113,000 lux the mutant and normal leaves showed similar rates of CO2 fixation per unit area of leaf surface, but on a chlorophyll basis the mutant leaves were twice as active. Hill reaction measurements on isolated chloroplasts also showed that the mutant chloroplasts werc saturated at higher intensities than the normal, and that the activity of the mutant was at least double that of the normal on a chlorophyll basis.It is suggested that the photosynthetic units of the mutant chloroplasts contain about half the number of chlorophyll molecules as compared to the normal photosynthetic units.Electron microscopy of leaf sections of normal and mutant leaves showed that the mutant chloropla,sts oontain fewer lamellae per chloroplast and fewer lamellae per granum. The lethal chloroplasts, which were virtually devoid of chlorophyll, were characterized by an absence of grana.

High Photosynthetic Rate of a Chlorophyll Mutant of Cotton

“…The rates of photosynthetic CO2 uptake/dm2 hr for the mutant and wild-type leaves are about equal to those found in cotton leaves at 600 /A/1 Co2,42 to 45 mg CO, fixed/dm2 hr (9). As shown in Table I (3,11,20) and in this respect approaches the rate of CO2 fixation of C4 plants. The light level necessary to saturate photosynthesis in some chlorophyll-deficient mutants is similar to the level necessary to saturate photosynthesis in C, plants.…”

“…The lower chlorophyll content of the mutant cotton leaves, unlike the low chlorophyll content of pea and tobacco (11,19), does not lead to a lower photosynthetic rate at low light levels using tungsten lamps. The higher light levels required for the saturation of photosynthesis in pea and tobacco mutants are also different than photosynthesis in the cotton mutant.…”

“…This mutant shows a quantum yield equal to the wild-type at low light levels but shows a high quantum yield at high light levels. Highkin et al (10) rate of a pea mutant on a chlorophyll basis is higher than the wild-type at high light levels but lower at low light levels.…”

“…Schmid and Gaffron (21) have shown that the quantum yield of the tobacco JWB mutant is less than the JWB wild-type over two broad regions of the spectrum. Schmid and Gaffron (19) and Highkin et al (11) conclude that the high photosynthetic rates (8,12).…”

“…There have recently been a number of investigations on the photosynthetic characteristics and high photosynthetic rates of different chlorophyll mutants (2-4, 10,11,13,14,[17][18][19][20][21]25). Most of the chloroplasts of these mutants show a high proportion of stroma lamellae, and the reduced chlorophyll content may be related to this deficiency of grana.…”