Question

after which of the following mineral the plan lose, the sympton of deficiency will appear in the old leaves rather than in the new leaves?

1. Zn 2.Fe 3.Mn 4.K. the official answer is K. How to explain this phenomona?

Answer 1

The important role of potassium:

It functions as a regulator in various metabolic processes like growth regulation. It helps in “protein synthesis”, photosynthesis, enzyme activation, solute transport, and ionic balance.

Potassium deficiency in leaves leads to a reduction in growth and subsequently other symptoms develop. When there is more demand of potassium in expanding roots then this increased demand is seen on oldest leaves as they start appearing yellowish but the new leaves grow with their normal green color and other properties like leaf size and texture.

Potassium deficiency makes the oldest leaves yellow at their “marginal” and “interveinal” zones. This phenomenon is called “chlorosis” of older leaves that finally spread to the entire “leaf blade”. This yellowing or chlorosis affects mature to old leaves and mostly the leaves those are present on the “axillary shoots”.

The appearance of potassium deficiency in older leaves occurs first than in new leaves because potassium is a “mobile element” as a result of which potassium can be translocated to the new leaves whenever the plant is deficient of the nutrient.