Grapevine under nutrient stress: exploring the adaptive mechanisms in response to iron deficiency conditions

Abstract

In plants, stress due to nutrient deficiency can significantly impair their development and productivity. Although iron is abundant in most soils, factors such as high pH and lime content affect Fe solubility, resulting in a remarkable reduction in plant growth and yield. In vineyards, several strategies have been used to prevent the occurrence of Fe deficiency chlorosis, including the use of Fe-chlorosis tolerant rootstocks. In response to low Fe availability, grapevine rootstocks adapt on several levels to maintain the required Fe level, however, the mechanisms underlying such changes are still unclear. Therefore, we sought to identify the key adaptive responses evolved by tolerant grapevine rootstock to cope with Fe limitation and to understand how different pathways interact to regulate Fe acquisition and transport in response to Fe shortage stress at the transcriptional level. Rooted woody cuttings of Fercal (tolerant) and 3309C (susceptible) rootstocks were used to study plant responses to i) direct Fe deficiency.

(-Fe) and ii) bicarbonate-induced Fe deficiency (+Fe+BIC) compared to iii) sufficient Fe supply (+Fe). Plants were grown in sand-filled pots for 30 days and watered daily with a modified half Hoagland nutrient solution according to the treatments applied. Our results revealed a difference in the response mechanisms evolved by both rootstocks, which further differed by the cause of Fe deficiency. Most severe symptoms of chlorosis were observed with the susceptible rootstock 3309C on young leaves, which was related to the significant decrease in chlorophyll content. Fercal plants showed higher ability to increase root biomass compared to 3309C plants under bicarbonate stress. This observation was confirmed by the increased expression of several genes involved in root growth and development such as (VvSAUR66, VvZAT6). In addition, Fercal roots were able to maintain constant level of ferric chelate reductase activity under both applied stress treatments compared to +Fe roots, while 3309C roots suffered a decrease in its activity under the same stresses. Moreover, under both Fe deficiency treatments, Fercal showed high efficiency in Fe transport and translocation through enhanced expression of related genes (e.g. VvOPT3, VvFRD3) compared to 3309C. The outcomes of this study will strengthen the current understanding of Fe deficiency induced adaptation, which can be used as an approach to develop Fe deficiency tolerant plants.