Plant Growth Calculators

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Plant growth is the irreversible increase in size, cell number, or dry matter of a plant over time. It occurs primarily at meristems — groups of undifferentiated cells capable of cell division — located at root tips, shoot tips (apical meristems), and lateral buds (axillary meristems). Plant growth is regulated by five major classes of hormones: auxins (cell elongation), cytokinins (cell division), gibberellins (stem elongation, seed germination), abscisic acid (dormancy, drought response), and ethylene (fruit ripening, senescence). Growth is measured by height, leaf area, dry biomass, or specific growth indices (relative growth rate, net assimilation rate).

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Plant Growth Hormones

  • Auxins (IAA): Produced in apical meristems; promote cell elongation; positive phototropism and gravitropism; suppress axillary bud growth (apical dominance); root initiation
  • Cytokinins: Promote cell division; produced in roots; transported upward; delay leaf senescence; promote lateral bud release
  • Gibberellins (GA): Promote stem elongation; break seed dormancy; stimulate flowering; semi-dwarf Green Revolution varieties have reduced GA response (Rht gene)
  • Abscisic acid (ABA): Stress hormone; closes stomata during drought; promotes seed dormancy; inhibits growth
  • Ethylene: Gas; promotes fruit ripening; senescence; wound response; epinasty

Growth Stages

Germination → seedling → vegetative growth → reproductive (flowering) → fruit/seed development → senescence. Determinate growth: fixed number of leaves/nodes (annual crops). Indeterminate: continuous growth (many trees, climbing plants).

Measuring Plant Growth

Height/leaf area: non-destructive; fast. Dry biomass: destructive; harvest, dry at 70°C, weigh. RGR = (ln W₂ − ln W₁)/(t₂−t₁). LAI: leaf area per unit ground area.

Glossary

Apical Meristem
Zone of actively dividing cells at root and shoot tips; source of primary growth (lengthening); produces auxin; apical dominance suppresses lateral bud growth via auxin signal.
Auxin (IAA)
Primary plant growth hormone promoting cell elongation; produced in shoot apex; drives phototropism and gravitropism; apical dominance; root initiation; binds TIR1/AFB receptors.
Gibberellins (GA)
Plant hormones promoting stem elongation and seed germination; DELLA protein degradation mediates response; semi-dwarf Green Revolution varieties have reduced GA sensitivity (Rht, sd1 genes).

Frequently Asked Questions

Plant growth is the irreversible increase in size through cell division and cell expansion. Primary growth: occurs at apical meristems (tips of roots and shoots) → lengthening of roots and shoots. Lateral root initiation from pericycle cells. Secondary growth: occurs at lateral meristems (vascular cambium, cork cambium) → thickening of stems and roots (wood formation in trees). Meristematic cells are totipotent — they can divide and differentiate into all cell types. After cell division: new cells elongate → driven by turgor pressure against cell walls (wall loosening by expansins); cell expands 10–1,000 × original volume. This elongation is the primary cause of stem and root lengthening.

Auxins (primarily indole-3-acetic acid, IAA) are the primary growth-promoting hormones: Cell elongation: IAA binds to its receptor (TIR1/AFB F-box proteins) → degrades transcriptional repressors (AUX/IAA) → activates growth genes including expansins (wall-loosening proteins). The growing tip (apical meristem) is the primary auxin source. Phototropism: light on one side → auxin moves to shaded side → cells on shaded side elongate more → bending toward light. Gravitropism: in horizontal roots → auxin accumulates on lower side → inhibits root elongation → root curves downward (auxin concentration for root growth inhibition is lower than for shoot promotion). Apical dominance: high auxin from shoot apex → suppresses axillary (lateral) bud growth; removing the shoot apex → auxin drops → axillary buds activate → bushy growth.

Abscisic acid (ABA) is the primary stress hormone: In drought: water deficit → ABA synthesis in roots and leaves. ABA transported to guard cells → activates anion channels → K⁺ and anion efflux from guard cells → turgor loss → stomatal closure → reduces transpiration. Signal transduction: ABA → PYR/RCAR receptors → inhibit PP2C phosphatases → ABA-activated protein kinases (SnRK2) → activate SLAC1 anion channel → stomatal closure. Seed dormancy: high ABA in maturing seeds promotes dormancy → seed waits for favorable germination conditions → ABA levels fall when conditions are right. Bud dormancy: ABA promotes dormancy in response to shortening days and cooling temperatures in perennial plants.

Gibberellins (GAs): over 130 structurally related compounds; GA₁ and GA₄ most bioactive in plants. Stem elongation: GA promotes elongation by stimulating both cell division and cell expansion via DELLA protein degradation. Semi-dwarf varieties: Green Revolution wheat and rice have reduced GA response (Rht genes in wheat; sd1 gene in rice → reduced DELLA degradation) → shorter straw → less lodging → more responsive to fertilizer → higher yield. Seed germination: GA promotes amylase production in the aleurone layer of cereal seeds → starch hydrolysis → provides energy for the embryo. Vernalization/flowering: GA promotes flowering in some plants after cold treatment. Agricultural uses: applied to seedless table grapes → berry enlargement (Thompson seedless); applied to barley in malting → increases enzyme production for brewing.