Sink strength of citrus rootstocks under water deficit

Abstract

Carbon allocation between source and sink organs determines plant growth and is influenced by environmental conditions. Under water deficit, plant growth is inhibited before photosynthesis and shoot growth tends to be more sensitive than root growth. However, the modulation of source-sink relationship by rootstocks remain unsolved in citrus trees under water deficit. Citrus plants grafted on Rangpur lime are drought tolerant, which may be related to a fine coordination of the source-sink relationship for maintaining root growth. Here, we followed 13C allocation and evaluated physiological responses and growth of Valencia orange trees grafted on three citrus rootstocks (Rangpur lime, Swingle citrumelo and Sunki mandarin) under water deficit. As compared to plants on Swingle and Sunki rootstocks, ones grafted on Rangpur lime showed higher stomatal sensitivity to the initial variation of water availability and less accumulation of non-structural carbohydrates in roots under water deficit. High 13C allocation found in Rangpur lime roots indicates this rootstock has high sink demand associated with high root growth under water deficit. Our data suggest that Rangpur lime rootstock used photoassimilates as sources of energy and carbon skeletons for growing under drought, which is likely related to increases in root respiration. Taken together, our data revealed that carbon supply by leaves and delivery to roots are critical for maintaining root growth and improving drought tolerance, with citrus rootstocks showing differential sink strength under water deficit.

Effect of Three Water Regimes on the Physiological and Anatomical Structure of Stem and Leaves of Different Citrus Rootstocks with Distinct Degrees of Tolerance to Drought Stress

“…Rootstock choice and selection for the citrus scion variety are the most valuable decisions for growers for the implication of better yield and quality with other valuable characters. Citrus rootstock controls the physiological, biochemical, morphological, and genetic characteristics of scion cultivars grafted on selected rootstocks through the rootstock scion interaction pathway [3]. Fruit juice quality and tree productivity of scion cultivars are also affected by rootstock characters.…”

Metabolic profiling of drought tolerance: revealing how citrus rootstocks modulate plant metabolism under varying water availability

“…Interestingly, the initial decline in substrate moisture also stimulated Rangpur lime root growth, a morphological strategy to improve water uptake that is supported by enhanced photoassimilate supply to roots under drought (Silva et al, 2021). Overall, Rangpur lime roots were more sensitive and responded rapidly to water deficit, anticipating morphological and physiological reactions before a more drastic reduction in water availability, as described in previous studies (Santana-Vieira et al, 2016; Miranda et al, 2020; Silva et al, 2021). Despite a significant inhibition of growth at phase I, shoot growth resumed at phase II and was maintained at high rates during rehydration ( Fig.…”

“…Among citrus rootstocks, Rangpur lime ( Citrus limonia Osbeck) is known by its drought tolerance linked to morpho-physiological strategies to maintain shoot water status, leaf gas exchange and plant growth under water deficit (Mourão Filho et al, 2007; Ribeiro and Machado, 2007; Pedroso et al, 2014; Miranda et al, 2018; Bowman and Joubert, 2020; Miranda et al, 2021; Silva et al, 2021). Rangpur lime presents high root hydraulic conductivity and internal hydraulic redistribution (Medina and Machado, 1998; Medina et al, 1998; Miranda et al, 2018; Miranda et al, 2021), besides being able to detect subtle variations in water availability (Santana-Vieira et al, 2016; Miranda et al, 2020; Silva et al, 2021). These traits improve shoot water balance and together with an effective stomatal regulation favor leaf gas exchange under water deficit.…”

“…In fact, plants need a fine tuning to reduce water loss while maintaining photosynthesis, which modifies growth pattern to balance energy supply and demand under varying water availability (Flexas et al, 2006; Chaves and Oliveira, 2004; Smith and Stitt, 2007). Increased sink demand by photoassimilates and enhanced root growth under water deficit are other two important morpho-physiological responses of Rangpur lime to water deficit (Pedroso et al, 2014; Silva et al, 2021). However, underlying metabolic processes that support the drought tolerance syndrome found in Rangpur lime have not been fully elucidated.…”

Grafting enhances plants drought resistance: Current understanding, mechanisms, and future perspectives

“…Besides accumulating greater root biomass, drought-resistant rootstocks display higher root plasticity and root vigor than drought-sensitive ones ( Han et al., 2019 ; Silva et al., 2021 ). Maintaining the rapid growth and large roots under water stress is important for drought-resistant improvement ( Li et al., 2020 ).…”