Copper deficiency in Helianthus annuus L.: developmental and metabolic consequences, stomatal function and senescence

The effects of copper deficiency on developmental morphology and on age related metabolic activity, water utilization, stomatal response to light and leaf senescence in the sunflower, Helianthus annuus L., were monitored by sampling single leaves representing each leaf pair at designated harvest times during much of the vegetative lifespan. Plants grown in nutrient solutions lacking copper exhibited no apparent abnormalities during early vegetative growth and leaf morphology differed little from controls. There were no significant differences in rates of respiratory oxygen uptake of basal leaves between minus copper and controls. The effects of copper deficiency on rates of photosynthetic oxygen evolution were related to leaf age: rates were lower than controls in young basal leaves but higher as these leaves approached senescence. Both respiration and photosynthesis were more susceptible to KCN inhibition in minus copper leaves than in controls. There were no differences in cumulative water use per plant during the first five weeks after transfer of seedlings to nutrient solutions and only minor differences in stomatal aperture and guard cell potassium levels in ambient greenhouse light. Both minus copper and control leaves exhibited a sequential loss of stomatal function. Decay in the turgor driven opening response to light preceded loss of light dependent uptake of potassium into guard cells. Both changes in stomatal response to light occurred before major breakdown of chlorophyll. Basal leaves of sunflowers grown in minus copper nutrient solution tended to be retained longer and exhibited delayed loss of chlorophyll.