Sugar Input, Metabolism, and Signaling Mediated by Invertase: Roles in Development, Yield Potential, and Response to Drought and Heat  Ruan Yong-Ling , Jin Ye , Yang Yue-Jian , Li Guo-Jing , Boyer John S.   Molecular Plant  Volume 3, Issue 6, Pages 942-955 (November 2010) DOI: 10.1093/mp/ssq044 Copyright © 2010 The Authors. All rights reserved. Terms and Conditions

Figure 1 A Schematic Diagram of Invertase-Mediated Sucrose Degradation in Sinks. Phloem unloading of sucrose (S) in sinks may occur either apoplasmically into cell wall matrix or symplasmically through plasmodesmata (PD) in recipient cells. In the former case, unloaded sucrose could be hydrolyzed by cell wall bound invertase (CWIN) into glucose (G) and fructose (F) before being taken up by membrane bound hexose transporters (blue circles). Symplasmically imported sucrose or that taken up by membrane bound sucrose transporters (brown circles) may be hydrolyzed by cytoplasmic invertase (CIN). In some sinks, cytosolic sucrose is taken up into vacuoles (V), where it is hydrolyzed by vacuolar invertase (VIN). Both CWIN and VIN are subject to post-translational inhibition by their inhibitors (INH). The intracellular G+F may be (1) metabolized or (2) stored in the vacuole or for synthesis of sugar polymers such as starch and cellulose, or (3) sensed by nuclei (n)-localized hexokinase or transcription factors to regulate gene expression. Molecular Plant 2010 3, 942-955DOI: (10.1093/mp/ssq044) Copyright © 2010 The Authors. All rights reserved. Terms and Conditions

Figure 2 Developmentally Programmed and ABA-Induced Leaf Senescence Is Blocked by Enhancement of CWIN Activity through Silencing Its Inhibitor in Tomato. (A) Compared to a null plant on the right, silencing the expression of a CWIN inhibitor, INVINH1, delayed leaf senescence (left). (B) ABA-induced leaf senescence (yellowing) in source leaf (left). The induction was blocked in the INVINH1-silenced transgenic plant (right). The image was reproduced from Jin et al. (2009). (C) A model of INVINH1/CWIN-regulated leaf senescence in null or wild-type plant. Here, INVINH1 expression increases as the leaf ages, which reduces CWIN activity and consequently may decrease the hexose-to-sucrose ratio in the leaf apoplasm. The low glucose and fructose concentration in the cell wall may serve as a signal to (1) allow ABA-induced leaf aging to proceed and (2) induce the expression of senescence-related genes (LeSENUs) such as Cys-protease for N-remobilization to other plant bodies. (D) A model of delayed leaf senescence in INVINH1-silenced transgenic plant. Silencing INVINH1 expression recovers CWIN activity in ‘old’ leaves to the young leaf level. This may increase the hexose-to-sucrose ratio in the leaf apoplasm. The high glucose and fructose concentration in the cell wall may serve as a signal to block ABA-induced leaf aging and the expression of senescence-related genes (LeSENUs), hence senescence. See text and Jin et al. (2009) for more details. Molecular Plant 2010 3, 942-955DOI: (10.1093/mp/ssq044) Copyright © 2010 The Authors. All rights reserved. Terms and Conditions

Figure 3 Net Photosynthesis (Closed Circles) and Respiration (Open Circles) during Progressive Water Deficits (Low Leaf Water Potentials) in Sunflower, Maize, and Soybean. Data are for the entire shoot and are redrawn from Boyer (1970). Molecular Plant 2010 3, 942-955DOI: (10.1093/mp/ssq044) Copyright © 2010 The Authors. All rights reserved. Terms and Conditions

Figure 4 Ovary Biochemistry during a Water Deficit in Maize around the Time of Pollination. (A–F) Hydrated controls. (G–M) Water deficient plants. (N–S) Water-deficient plants whose stems were fed sucrose during the water deficit. In controls (A–F), CWIN was situated in the pedicel below the nucellus (A, dark stain) while VIN was in the nucellus (B, dark stain). Starch (dark stain) was in the ovary wall and pedicel but absent in the nucellus (C, dark stain), while glucose was abundant in the same tissues but also present in the nucellus in low concentrations (D, red highest, blue lowest concentration). Phloem terminated in the pedicel below the nucellus (E, white auto-fluorescence) and thus the location was similar to that for CWIN, starch, and glucose. Grain yield was high (F). During a water deficit (low Ψw, G–M), the enzyme activities, starch content, and glucose concentration were low and grain yield was negligible at maturity (M), indicating widespread abortion. However, if sucrose was fed to the stems during the water deficit (low Ψw Fed Sucrose, N–S), all of these activities and metabolites recovered somewhat. Abortion was largely prevented (S, grain numbers were 68% of controls). The water deficit and feeding extended for 6 d and resulted in leaf Ψw of about –1.5 MPa, which inhibited photosynthesis, as shown in Figure 3. Images above were taken during the water deficit on the day of pollination. Water was supplied after the 6-d deficit. From McLaughlin and Boyer (2004a, 2004b) and Zinselmeier et al. (1999). Molecular Plant 2010 3, 942-955DOI: (10.1093/mp/ssq044) Copyright © 2010 The Authors. All rights reserved. Terms and Conditions