Variation in Photosynthesis and Enzyme Activity in Cenchrus ciliaris L.

Populations of Cenchrus ciliaris differ significantly in relativegrowth-rate (R), net assimilation rate (E), and leaf-area ratio(F). Differences in R were related to differences in E ratherthan in F. The populations also differed in the rate of apparentphotosynthesis of individual leaves as measured by infra-redgas analysis. Warburg and ^l4CO₂ techniques. Temperature andlight-response measurements revealed optimum temperature forphotosynthesis of 35 °C and the rate in most populationscontinued to increase up to the highest levels of irradianceemployed (200 W m²). The relative order of the populations wassimilar in all methods of analysis, but there was no relationshipevident between leaf photosynthesis and E derived from growthanalysis. The activity of the enzyme PEP carboxylase, expressedin terms of unit leaf area, was correlated with photosyntheticrate of the leaf. Activities of PEP carboxylase and of proteinsynthesis in vitro expressed on a basis of soluble protein contentwere correlated with E, but no such relationship was found forthe enzymes acid phosphatase and alanine--ketoglutarate aminotransferase.     

A Manometric Technique for Determination of Apparent Photosynthesis of Lolium

A manometric technique for measuring photosynthesis of detachedleaves of Lolium is described. Results are compared with infra-redgas analysis data and ¹⁴CO₂ assimilation by attached leavesfrom similar plant material. All three methods gave similarcomparative estimates of apparent photosynthesis.     

Effect of Temperature on the Activity of Carboxylases in Tropical and Temperate Gramineae

Temperate Gramineae show maximal net photosynthesis at 20–5°C, whereas tropical Gramineae have maxima between 30 and35 °C. Moreover, it has been suggested that different carboxylationreactions are involved in the two groups. The present studyof the temperature dependance of in vitro ribulose-1,5- diphosphate(RuDP), and phosphopyruvate (PEP) carboxylases indicates thatthe two enzymes have clearly marked differences in temperaturesensitivity. RuDP carboxylase, present in the temperate andtropical species studied, showed maximal activity around 20–5°C except in Zea. By contrast, PEP carboxylase activityin all species was maximal between 30 and 35 °C. The dataimply that activity and temperature sensitivity of the relevantcarboxylase enzymes may well be a significant limiting factorin leaf photosynthesis, even at light saturation.     

Effects of Low Oxygen on Photosynthesis, Translocation and Growth in Green Pepper (Capsicum annuum)

Green pepper (Capsicum annuum cv. Bell Boy) plants were exposedin chambers to low (2%) oxygen and controlled carbon dioxideconcentrations. Vegetative and fruiting plants showed short-termincreases in net photosynthesis in low oxygen or elevated carbondioxide (up to 900 µl CO₂ l^–1). Photosynthesis ofyoung vegetative plants increased in low oxygen in the short-termbut there was no long-term benefit. Low oxygen enhancement ofphotosynthesis declined with time and after 10 d, leaf areaand root dry weight were less than in plants grown in normalair. Labelled assimilates were translocated from leaves to otherregions at similar rates in low oxygen and normal air. Low oxygenreduced respiratory losses from leaves and reduced the proportionof soluble carbohydrate converted to polysaccharide in all plantparts. Thus, low-oxygen environments decrease the utilisationof assimilates which then may lead to inhibition of photosynthesis. Capsicum annuum, photosynthesis, photorespiration, translocation, utilization of assimilates