Fat Metabolism in Germinating Citrullus vulgaris. Part II

Breakdown of fat in watermelon seedlings germinated in the darkoccurs in essentially the same way as in the light. Free fattyacids do not accumulate and the composition of the lipid remainsalmost unchanged during its rapid utilization. The low weight of ‘protoplasmic lipid’ remainingin the etiolated cotyledons after the storage fat has disappearedcontains a lower proportion of linolenic acid than that fromgreen cotyledons of a corresponding age. The weight of phosphatide (lipid P) per cotyledon increases both in light- anddark-grown seedlings until 8 days, thereafter declining in thedark but continuing to rise in the light. Phosphatide and glyceridefractions from the same fat resemble each other fairly closelyin fatty acid composition.     

Carbon Dioxide Exchange, Soluble Carbohydrates and Acid Accumulation in a Fructan Accumulating Plant: Fourcroya humboldtiana Treal.

Fourcroya hunboldtiana Treal. (Agavaceae) is a rosette plantwhich accumulates fructans and shows active CAM metabolism undernatural conditions. Daily changes in titratable acidity wererelated to leaf age and degree of leaf inclination. Nocturnalacidification rates of 15 mmol H+ g–1 fresh weight h–1were measured under natural conditions and no recycling of respiratoryCO₂ could be detected. Fructans of low molecular weight apparentlyconstituted the only source for the synthesis of substrate forCO₂ fixation. Acidification was accounted for by the amountof external CO₂ fixed and the reduction in fructan content duringthe night. The maximum degree of polymerization of fructansas shown by differential extraction in alcoholic solutions ofdecreasing concentration, changed during the CAM cycle, at theend of the night period maximum degree of polymerization wasaround 24, while in the late afternoon the degree of polymerizationincreased up to 43. Key words: Fourcroya humboldtiana Treal., fructans, CAM metabolism