Effects of Exogenous Putrescine on Mycorrhiza, Root System Architecture, and Physiological Traits of Glomus mosseae-Colonized Trifoliate Orange Seedlings

Abstract

Putresince (Put) as one of the important polyamines (PAs) has been identified to regulate mycorrhizal development of citrus plants. The present study was to screen an efficient concentration of Put application at the range of 0.05-1 mM on the trifoliate orange (Poncirus trifoliata) seedlings colonized by Glomus mosseae, in terms of growth, root system architecture, and chlorophyll and carbohydrate contents. Compared to the non-Put treatment, all the Put treatments, especially 0.05 mM Put, significantly increased mycorrhizal colonization of tap root in addition to first, second, and third order lateral roots. The mycorrhizal seedlings treated by 0.05, 0.1, and 1 mM Put showed greater growth (stem diameter, height, leaf number, and fresh mass) and root morphological properties ( tap root length, projected and surface areas, and volume) and higher numbers of first, second, and third order lateral roots. Bio-molecules like chlorophyll a, total chlorophyll, and carotenoid contents of the seedlings were significantly increased by the Put treatments at 0.05-1 mM. All exogenous Put application at the range of 0.05-1 mM significantly decreased sucrose contents but increased glucose contents of leaves and roots. This study suggests that exogenous Put can significantly improve growth performance and root system architecture, besides changes in physiological traits of AMF seedlings. The 0.05 mM concentration of Put showed the best effects.

Citrus Polyamines: Structure, Biosynthesis, and Physiological Functions

“…PAs did not improve the root length of all diameters, but only the diameters below 0.4 mm (more precisely, diameters 0.2-0.4 mm) [35]. Nevertheless, PAs treatment did not affect the root average diameter [37], but sometimes it was decreased in PAs-treated plants [35,40]. The reduction in the average root diameter might be due to the increase in fine roots (%) and the decrease in coarse roots [40].…”

“…These effects may be associated with the well-known role of PAs in the regulation of cell Likewise, the addition of PAs to a medium containing Murashige and Skoog salts significantly improved the root formation and growth of two sweet orange cultivars (C. sinensis 'Pineapple' and 'Pêra') in a concentration-based manner [36]. Furthermore, PAs supplementation increased the numbers of first, second, and third-order lateral roots in PAs-treated plants [35,37] indicating that PAs regulate the root system architecture via controlling the formation and development of lateral root primordia. These effects may be associated with the well-known role of PAs in the regulation of cell division and differentiation in the root apex, and during lateral and adventitious root formation [87].…”

“…However, our knowledge about these roles is still limited, and in fact, many roles have not yet been discovered. These processes including somatic embryogenesis [33,34,96], seed germination [97], plant growth (including biomass production, plant height, fresh and dry weight, and number of leaves/plant) [35,36,44,45,47], root morphogenesis and architecture [35][36][37][38][39][40][41][42], photosynthesis and photosynthetic pigments [35,37,45,60], and reproductive development during flowering [49][50][51]88] and fruit set [55,71,88,98]. In the next paragraphs, we will discuss the multi-regulatory roles of PAs in citrus plants.…”

“…In citrus, several studies have outlined the role of PAs in root formation, morphology, and architecture [35][36][37][38][39][40][41][42] (Figure 3). In general, modifications of the endogenous levels of PAs by chemical inhibitors [36,39], by mutation or gene manipulation [74,112], or by exogenous supplementation [35][36][37]40,41] can directly affect the root morphogenesis, development, and subsequent architecture. The exogenous supplementation of PAs increased root length, root projected surface area, root volume and root tip number in Canton lemon (C. limonia) [35,40], C. tangerine seedlings [41], and trifoliate orange (P. trifoliata) seedlings [37].…”

“…In general, modifications of the endogenous levels of PAs by chemical inhibitors [36,39], by mutation or gene manipulation [74,112], or by exogenous supplementation [35][36][37]40,41] can directly affect the root morphogenesis, development, and subsequent architecture. The exogenous supplementation of PAs increased root length, root projected surface area, root volume and root tip number in Canton lemon (C. limonia) [35,40], C. tangerine seedlings [41], and trifoliate orange (P. trifoliata) seedlings [37]. PAs did not improve the root length of all diameters, but only the diameters below 0.4 mm (more precisely, diameters 0.2-0.4 mm) [35].…”