Nutrient seed priming improves abiotic stress tolerance in Zea mays L. and Glycine max L.

Abstract

Seed reserves are the primary source of mineral nutrients for early seedling development. ?Nutrient seed priming? is a technique in which seeds are soaked in nutrient solution and subsequently dried back to initial moisture content for storage. It is an efficient approach to increase seed nutrient contents along with priming effects to improve seed quality, germination speed and seedling establishment. Various abiotic stresses, such as sub-optimal temperature, drought, submergence and soil pH extremes can seriously affect seedling establishment and nutrient acquisition at early growth stages. This thesis focused on the role and contribution of nutrient seed priming in plant growth and nutritional status in maize and soybean under conditions of limited nutrient availability and low root-zone temperature. Protocols for nutrient seed priming with Zn, Mn, Zn+Mn, B and P were optimised for application in maize and soybean seeds (B and P priming in maize only). Optimum priming durations of 24 h (maize) and 12 h (soybean) were identified for both plant species but in instead of submerging seeds in priming solutions slow imbibition between filter papers was essential for soybean to minimise development of abnormal seedlings to avoid imbibition damage. Nutrient concentrations were calculated according to water uptake to double the natural seed reserves of the respective micronutrients and 50% increase in phosphorus. However, final uptake of the micronutrients was generally much higher (+500-1000%) while it was lower for P (+20%). In case of soybean this could be attributed to a high Zn and Mn binding capacity of the seed coat, which adsorbed up to 60% of the primed nutrients. Particularly, Zn and Zn+Mn priming stimulated plant growth in hydroponic culture systems and to a lower extent also on a soil with low availability of P, Zn and Fe. This was associated with a high shoot translocation of the primed nutrients (Zn and Mn), which was most expressed in the hydroponic culture system. Combined priming treatments with Zn and Mn were usually less effective than Zn priming alone, suggesting an antagonistic interaction. By contrast, mobility of primed B was extremely low and B priming was completely ineffective. In soil culture also P priming moderately increased shoot biomass production by 10-20 %. However the efficiency of P priming was largely limited by the high P demand of the plants. Low root zone temperature (RZT) at early spring is a limiting factor for maize production in Central and Northern Europe. Nutrient acquisition, nutrient uptake and particularly root growth are severely affected at low RZT and the consequences of these growth depressions are often not completely compensated until final harvest. Model experiments in hydroponics and soil culture revealed that maize nutrient seed priming with Zn, Mn and Fe is a promising strategy to diminish the deficiency of specific nutrients, such as Zn, Mn and also P and to maintain plant growth under low RZT stress. This was mainly attributed to significantly increased root growth and particularly fine root production in plants grown from nutrient-primed seeds. Improved net photosynthesis of primed plants was mainly related with increased leaf area and preliminary results suggest a higher tolerance to oxidative damage due to increased production of protective phenolics. Two independent field experiments under conditions of suboptimal temperatures during germination and early growth revealed an increase in grain yield of 10 ? 15 % for plants derived from Zn+Mn and Fe primed seeds. This finding demonstrates long-lasting persistence of priming effects. The molecular and physiological mechanisms behind require further investigation.

Samenreserven sind die primäre Quelle für die Mineralstoffversorgung während der frühen Keimlingsentwicklung. Nährstoffpriming ist ein methodischer Ansatz, bei dem Saatgut in Mineralstofflösungen vorgequollen und anschließend zur weiteren Lagerung auf Ausgangsfeuchte zurückgetrocknet wird. Hierdurch ist es möglich, neben vorquellungsbedingten Primingeffekten auch die Mineralstoffreserven zur Verbesserung der Saatgutqualität zu erhöhen sowie die Auflauf-Geschwindigkeit und die Keimlingsentwicklung zu verbessern, die durch verschiedenste Stressfaktoren, wie suboptimale Temperaturbedingungen, Trockenheit, Staunässe und pH-Extreme beeinträchtigt werden kann. Die vorliegende Arbeit beschäftigt sich mit der Wirkung von Nährstoffpriming auf das Wachstum und den Ernährungsstatus von Mais und Soja unter Bedingungen eingeschränkter Nährstoffverfügbarkeit und niedriger Wurzelraumtemperatur. Für die Saatgutapplikation von Zink (Zn), Mangan (Mn), Mn+Zn, Bor (B), Eisen (Fe) und Phosphat (P) bei Mais und Soja wurden Primingprotokolle entwickelt. Bei beiden Pflanzenarten ergab sich eine optimale Behandlungsdauer von 24 h. Jedoch war es notwendig, das Soja-Saatgut anstelle von submerser Inkubation in den Nährlösungen, langsam in Nährlösungsgetränktem Filterpapier einzuquellen, um die Entwicklung abnormaler Keimlinge aufgrund von Quellungsschäden zu vermeiden. Anhand der Wasseraufnahme der Keinlinge wurden die Nährlösungskonzentrationen so berechnet, das sich nach Einquellen eine Verdopplung der natürlichen Mineralstoffreserven im Samen ergeben sollte. Jedoch wurden für die Mikronährstoffe erheblich höhere Aufnahmeraten gemessen (+500 - 1000%), während die Aufnahme von P geringer war (+ 20%). Bei Soja konnte gezeigt werden, das die erhöhten Mikronährstoffgehalte auf eine hohe Bindungskapazität der Zwei unabhängige Feldversuche bei suboptimaler Temperatur während der Keimphase und des Jugendwachstums ergaben Kornertragssteigerungen von 10-15 % bei Mais nach Saatgutpriming mit Zn+Mn oder Fe. Diese Ergebnisse belegen die Langzeitwirkung der Primingeffekte. Die molekularen und physiologischen Grundlagen erfordern allerdings noch weitere Untersuchungen.