Carotenoids In contrast yellow pigments increase light absorption so that more light can get to the chloroplasts. My more tropical Passiflora, which lose all their leaves when put outside after winter, start in low light conditions with very yellowy (chlorotic) leaves which become greener as light levels increase. This chlorosis is often mistaken for a nutritional deficiency... we are conditioned to think that a nice dark green is normal, but if conditions are abnormal the leaf colour may also change from the norm. Passiflora also as climbers tend to shed leaves at the lower ends of the stem quite quickly as stronger light becomes available above. This rapid yellowing and dropping can lead to people thinking their plants are ill when they are not. Yellow pigments are also used by some Passiflora for egg mimicry on the leaves, see P. pardifolia. Healthy looking leaves with yellow edges as in the picture of P. coriacea above, after being repeatedly exposed to full sun when the temperature was 38°C/100°F in the shade, suggest overheating as the Mg+ magnesium ion in the chlorophylls is replaced by a hydrogen ion and the chlorophyll breaks down...in the same way as when we overcook vegetables they end up yellow. |
Passiflora pigments - carotenoids
