Extension growth of Impatiens glandulifera at low irradiance: Importance of nitrate and potassium accumulation

• Published in: Annals of botany Vol. 95; no. 4; pp. 641 - 648
• Main Authors: Andrews, M, Maule, H. G, Raven, J. A, Mistry, A
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.03.2005; Oxford Publishing Limited (England)
• Subjects: Acclimatization; Cytosol; extension growth; glucose; Glucose - metabolism; Greenhouses; height; Hexoses; Impatiens - growth & development; Impatiens - radiation effects; Impatiens glandulifera; Irradiance; Light; light intensity; malate; malic acid; nitrate; nitrates; Nitrates - metabolism; nutrient requirements; Original; ornamental plants; osmotic pressure; osmoticum; photon costs; Photons; plant growth; plant nutrition; Plants; potassium; Potassium - metabolism; Seasons; shade acclimation; shade tolerance; Stem cells; stems; Sugars; Vacuoles; Woodlands
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mci059

BACKGROUND AND AIMS: The summer annual Impatiens glandulifera can reach 3 m in height within deciduous woodland. The primary objective was to determine if NO3(-1)-N accumulation, and hence its osmotic effect, is an important physiological mechanism allowing Impatiens to achieve substantial height under low irradiance. METHODS: Stem extension, concentrations of K⁺ and NO3(-1)-N in leaves and concentrations of K⁺, NO3(-1)-N and other inorganic anions, malate, sugars, total N and total osmoticum in stem were measured in I. glandulifera sampled at different irradiance levels in deciduous woodland and in a glasshouse. Also, the energetic costs, as absorbed photons, of generating osmolarity in stem cell vacuoles with KNO₃, K₂malate or hexose sugar were determined. KEY RESULTS: Results were similar in the woodland and glasshouse. At 50-100 % relative irradiance (Ir; open ground PAR = 100 % Ir) and 2-10 % Ir, plant height increased from 7-14 cm to 130-154 cm in 64-67 d. Leaf and stem NO3(-1)-N concentrations were negligible at 50-100 % Ir while K⁺, malate²⁻ and sugars, respectively, accounted for 33·2-50·1 , 19·3-20·8 % and 2·0-2·6 % of total osmoticum in stems. At 2-10 % Ir, NO3(-1)-N concentrations were four to eight times greater in stems than leaves. Here, NO3(-1)-N constituted 26·7-34·3 % of the total osmotic concentration in the stem and NO3(-1)-N constituted 69-81 % of total N in stem tissue. Also at 2-10 % Ir, K⁺ comprised 44·9-45·9 % and malate plus sugars 2·2-3·1 % of total osmotic concentration. The energy cost of osmoticum as KNO₃ was calculated as less than half that of malate and less than one-seventh that for hexose. Further calculations suggest that use of KNO₃, K₂malate or glucose as osmoticum at low irradiance would, respectively, cost approx. 7 %, 16 % and 50 % of the total construction cost of the stem. CONCLUSIONS: It is concluded that accumulation of NO3(-1)-N in place of organic molecules in stems is an important mechanism allowing I. glandulifera to achieve substantial height at low irradiance.