They look hungry in those small pots.
If they are indoors with grow lights and are not auto's you can transplant to bigger pots and put them back under 18 hours of light to re veg them.
Its a mobile nutrient, so as it becomes deficient in a plant it will make its way up towards the newest growth. N def is always seen starting from the bottom and making its way up the plant. Its not irreversible during veg, but during the flower phase that level of deficiency will stunt the plant.