Changes in fatty acid composition of polar lipids associated with growth and senescence in leaves of Catharanthus roseus

Polar lipids are important membrane components of plant cells. They are known to affect certain membrane properties like permeability, fluidity and active transport. In the present study, individual leaf buds were tagged on the day of appearance and sampling began 7 days later. Additional samples were taken at 7 days intervals until leaf abscission occurred about 77 days after tagging. The experiments were performed from July to October, a time period characterized by a day length of 12 ± 1.5 h and average day and night temperature of approximately 30 and 20°C, respectively. The fatty acid composition of polar lipids from young, mature and senescent leaves of Catharanthus roseus was studied in the present study. Green leaves were observed to contain a considerable amount of hexadecatrienoic acid (16:3) in monogalactosyldiglyceride (MGDG), which suggests that C. roseus belongs to 16:3 plants. Further, the percentage of linolenic acid (18:3) in the chloroplast lipids was lower in senescent leaves than that of green tissues. Senescent leaves also had lower proportions of MGDG 16:3 and phosphatidyl glycerol (PG) hexadecanoic acid (16:1). Such selective catabolism of molecular species of these lipids may be suggestive of significant alterations in ultra structure of chloroplast membranes, thus probably affecting the accumulation of indole alkaloids in the leaf tissue. Besides, the age dependent alterations in the fatty acid composition of other polar lipids, namely, phosphatidyl choline (PC), phosphatidyl inositol (PI), phosphatidyl ethanolamine (PE), and phosphatidyl serine (PS) indicate the possibility of degradation of the organelles other than chloroplast (principally vacuoles) in the leaf cells.