Transport in Plants & Mineral Nutrition — Clinical/Applied Connections — Summary

Whiptail disease (cauliflower): caused by molybdenum (Mo) deficiency; leaves become strap-like with only the midrib remaining; Mo is required for both nitrogenase and nitrate reductase enzymes.
Internal cork disease (apple): caused by boron (B) deficiency; brown corky tissue develops internally in fruit; B is required for cell wall formation, pollen tube germination, and sugar transport.
Little leaf disease / Khaira disease of rice: caused by zinc (Zn) deficiency; Zn is required for auxin synthesis via the tryptophan pathway, so Zn-deficient plants have stunted internodes.
Grey speck of cereals (oats): caused by manganese (Mn) deficiency; Mn is required for the photolysis of water in Photosystem II.
Dieback of shoots: caused by copper (Cu) deficiency; Cu is part of plastocyanin (electron carrier in PS I) and cytochrome oxidase.
Leguminous crops (green manure): Rhizobium–legume symbiosis enriches soil nitrogen naturally. Farmers plant legumes in rotation to restore soil N levels without chemical fertilisers — a practice central to sustainable agriculture.
Azolla–Anabaena symbiosis: Anabaena (a cyanobacterium) lives in the leaf cavities of the aquatic fern Azolla. This symbiotic system is used as biofertiliser in paddy (rice) fields across South and Southeast Asia.
Guttation fluid: contains not just water but dissolved mineral salts and amino acids; visible as white salt deposits on leaf margins after the fluid evaporates — a practical indicator of active root pressure.
Wilting and ABA signalling: under water stress (drought), guard cells accumulate ABA, trigger $K^{+}$ efflux, lose turgor, and close stomata — reducing water loss. This is exploited in crop management by priming plants with ABA analogs.
Suberin and waterproofing: the Casparian strip functions like a biological gasket, preventing bypass of the selective mineral transport system — analogous to tight junctions in animal epithelial tissue.
Osmotic adjustment: plants in saline soil accumulate compatible solutes (proline, glycine betaine) to lower Ψs and maintain water uptake against high external solute concentrations — a tolerance mechanism relevant to salt-tolerant crop breeding.
Hydroponic culture: plants grown in nutrient solutions with precisely controlled mineral concentrations — the experimental system used to establish which elements are truly essential (Arnon and Stout criteria derived from such experiments).