Elements essential to growth and development of plants and the criteria for establishing the essentiality

HYDROPONICS- JULIUS VONSACHS

Criteria Absolutely necessary- life cycle of plant is affected Specific Direct involvement in metabolism

Present in large amounts

Trace elements- needed in small amounts

Structural elements of cell Components of Energy compounds Activate or inhibit enymes Affect osmotic potential

NITROGEN: Absorbed asNO3- needed for meristamatic cells Component of protein, NA,vitamins,hormones

Potassium: Absorbed potassium K+ ions Needed in the meristerm, bud, leaves and root tips. Anion-cation balance, opening and closing of stomata, turgidity of cells

Sulpher: in the form of sulphate. Present in aminoacids cysteine and methionine, coenzymes, vitamins and ferredoxin

Iron: as Fe3+. Needed in large amounts than other micronutrients. Constituent of protein, essential for the formation of chlorophyll

Zinc: Zn2+.synthesis of auxin

Critical concentration: the concentration below which the growth is retarded Morophological changes due to deficiency- deficiency symptoms. Deficiency symptom first appear in older parts in case of actively mobilised elements – nitrogen, potassium And in young tissues in case of relatively immobile- sulpher, calcium

Premature leaf fall. Stunted growth, inhibition of cell division

Concentration that reduces dry wight by 10% is toxic.

Absorption has two phases First into the outer space- apoplast pathway Second into the inner space- symplast pathway

Translocation takes place through transpirational pull

Majority nutrients get through weathering and breakdown of rocks. Soil harbours nitrogen fixing bacteria, other microbes, holds water, supplies air to roots.

Only certain prokaryotes are capable of fixing nitrogen- called biological nitrogen fixation Nitrogenase enzyme helps fixation Azotobacter, Beijernickia, Rhodospirillum, Bacillus are microbes fixing nitrogen Anabaena and Nostoc- cyanobacteria

NITROGENASE IS HIGHLY SENSITIVE TO OXYGEN. NEEDS ANAEROBIC CONDITION. NODULE CONTAIN OXYGEN SCAVENGER LEG -HAEMOGLOBIN

Ammonia is used for synthesis of amino acids