Resprouting as a response to disturbance is now widely recognized as a key functional trait among woody plants and as the basis for the persistence niche. However, the underlying mechanisms that define resprouting responses to disturbance are poorly conceptualized. Resprouting ability is constrained by the interaction of the disturbance regime that depletes the buds and resources needed to fund resprouting, and the environment that drives growth and resource allocation. We develop a buds-protection-resources (BPR) framework for understanding resprouting in fire-prone ecosystems, based on bud bank location, bud protection, and how buds are resourced. Using this framework we go beyond earlier emphases on basal resprouting and highlight the importance of apical, epicormic and below-ground resprouting to the persistence niche. The BPR framework provides insights into: resprouting typologies that include both fire resisters (i.e. survive fire but do not resprout) and fire resprouters; the methods by which buds escape fire effects, such as thick bark; and the predictability of community assembly of resprouting types in relation to site productivity, disturbance regime and competition. Furthermore, predicting the consequences of global change is enhanced by the BPR framework because it potentially forecasts the retention or loss of above-ground biomass.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12001

Resprouting as a key functional trait: how buds, protection and resources drive persistence after fire

Extracellular invertase is the key enzyme of an apoplasmic phloem unloading pathway and catalyses the hydrolytic cleavage of the transport sugar sucrose released into the apoplast. This mechanism contributes to long-distance assimilate transport, provides the substrate to sustain heterotrophic growth and generates metabolic signals known to effect various processes of primary metabolism and defence responses. The essential function of extracellular invertase for supplying carbohydrates to sink organs was demonstrated by the finding that antisense repression of an anther-specific isoenzyme provides an efficient method for metabolic engineering of male sterility. The regulation of extracellular invertase by all classes of phytohormones indicates an essential link between the molecular mechanism of phytohormone action and primary metabolism. The up-regulation of extracellular invertase appears to be a common response to various biotic and abiotic stress-related stimuli such as pathogen infection and salt stress, in addition to specific stress-related reactions. Based on the observed co-ordinated regulation of source/sink relations and defence responses by sugars and stress-related stimuli, the identified activation of distinct subsets of MAP kinases provides a mechanism for signal integration and distribution within such complex networks. Sucrose derivatives not synthesized by higher plants, such as turanose, were shown to elicit responses distinctly different from metabolizable sugars and are rather perceived as stress-related stimuli.

Extracellular invertase: key metabolic enzyme and PR protein

Extracellular invertase mediates phloem unloading via an apoplastic pathway. The gene encoding isoenzyme Nin88 from tobacco was cloned and shown to be characterized by a specific spatial and temporal expression pattern. Tissue-specific antisense repression of Nin88 under control of the corresponding promoter in tobacco results in a block during early stages of pollen development, thus, causing male sterility. This result demonstrates a critical role of extracellular invertase in pollen development and strongly supports the essential function of extracellular sucrose cleavage for supplying carbohydrates to sink tissues via the apoplast. The specific interference with phloem unloading, the sugar status, and metabolic signaling during pollen formation will be a potentially valuable approach to induce male sterility in various crop species for hybrid seed production.

https://www.pnas.org/content/pnas/98/11/6522.full.pdf

Induction of male sterility in plants by metabolic engineering of the carbohydrate supply.

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodging-resistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grain-filling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.

/pdf/activities-of-key-enzymes-in-sucrose-to-starch-conversion-in-5dm8bs9bf1.pdf

Activities of key enzymes in sucrose-to-starch conversion in wheat grains subjected to water deficit during grain filling.

Remobilization and transfer of the pre-stored food in vegetative tissues to the grains in monocarpic plants require the initiation of whole plant senescence. However, mechanisms by which plant senescence promotes remobilization of assimilates are rather obscure. This study examined the relationship between the senescence induced by water deficits and C remobilization during grain fill. Two semi-winter wheat cultivars (Triticum aestivum L.),Yangmai 158 and Yangmai 931, were treated with two levels of nitrogen (normal [NN] or high [HN]) and three levels of soil moisture (well-watered, moderate water deficit, and severe water deficit). Results showed that water deficits enhanced the senescence by accelerating loss of leaf nitrogen and chlorophyll and increasing lipid peroxidation. At maturity, 75 to 92% of pre-anthesis C stored in the straw was reallocated to grains in water-deficit treatments, 50 to 80% higher than the amount in well-watered treatments, indicating that water deficits promoted remobilization. The peak values of abscisic acid (ABA) in both leaves and grains under water-defidt treatments were 63 to 144% higher than those under well-watered treatments. The elevated ABA level correlated with the degree of earlier leaf senescence, the 14 C partitioning into grains, and the carbon remobllization. The activites of both add invertase (INV) and sucrose synthase (SS) in grains were also enhanced by water deficits at the midstage of grain fill. Our results suggest that the senescence and remobilization promoted by water defidts during grain fill are coupled processes in wheat, and elevated ABA concentration may play a regulative role.

Water Deficit–Induced Senescence and Its Relationship to the Remobilization of Pre-Stored Carbon in Wheat during Grain Filling

The activities of soluble invertase (EC 3.2.1.26), cell wall invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1.13) were determined in Easter lily (Lilium longiflorum Thunb. cv. Nellie White) floral organs during flower development. These enzyme activities were correlated with dry weight gains and carbohydrate pools to investigate the importance of their expression in maintaining sink strength of floral organs. In the early stages of flower bud development, anthers exhibited the highest rates of dry weight gain and activity of sucrolytic enzymes. Once anther growth was completed, the dry weight gain of tepal, filament, stigma and style increased with a concomitant increase in hexose concentrations and invertase activity. Although all three enzymes capable of catalyzing sucrose cleavage were present in every flower organ of L. longiflorum, soluble invertase was the predominant enzyme in all flower organs except stigma where cell wall invertase dominated. Soluble invertase activity was highly correlated with dry weight gain in most of the flower organs.

Sucrose-cleaving enzymes and carbohydrate pools in Lilium longiflorum floral organs

Summary


• 
A comprehensive analysis of nonstructural carbohydrates in storage organs (bulbs and corms) of 30 ornamental geophytes was conducted by employing a variety of extraction techniques followed by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD).

• 
Among species, starch, fructan, glucomannan and soluble sugars accounted for 50–80% of storage organ dry weight (DW). Starch ranged from 24 to 760 mg g−1 DW, fructan (commonly occurring with starch) from 25 to 500 mg g−1 DW, and glucomannan from 15 to 145 mg g−1 DW. An acid hydrolysis protocol for concurrent determination of fructan and glucomannan was developed. The average degree of polymerization (DP) of ethanol and water-soluble fructan and the man : glu ratio of glucomannan also varied between species.

• 
The 80% ethanol fraction contained soluble sugars and short-chain fructans (< 25 DP), whereas water extracts contained soluble sugars, fructans (both short- and long-chain, ≤ 100 DP), and glucomannan. A substantial portion of the starch became ‘soluble’ in water during extraction, and depended on the species and extraction temperature.

• 
Our results indicate that extraction and analysis techniques of nonstructural carbohydrates for physiological and biochemical research on geophytic storage organs should be validated to accurately understand the identity of diverse carbohydrate pools, their physiological relevance and functions.

https://www.jstor.org/stable/pdfplus/25150588.pdf

Analysis of nonstructural carbohydrates in storage organs of 30 ornamental geophytes by high-performance anion-exchange chromatography with pulsed amperometric detection.

/pdf/gibberellin4-7-benzyladenine-and-supplemental-light-improve-29k07zj0p8.pdf

Gibberellin4+7, Benzyladenine, and Supplemental Light Improve Postharvest Leaf and Flower Quality of Cold-stored `Stargazer' Hybrid Lilies

Preventive mechanisms of gibberellin4+7 and light on low-temperature-induced leaf senescence in Lilium cv. Stargazer

Summary
• Changes in the physical state of cellular water and its interrelations with carbohydrate metabolism were studied during preplanting storage of tulip bulbs (Tulipa gesneriana‘Apeldoorn’).
• Magnetic resonance imaging, light and scanning electron microscopy and high-performance anion exchange chromatography with pulsed amperometric detection were used to follow time-dependent changes during bulb storage at 17 or 20°C (nonchilled) or 4°C (chilled).
• No visible differences in scale structure and central bud development were observed microscopically between chilled and nonchilled bulbs. However, the scales of the chilled bulbs exhibited higher water content, faster starch degradation and increased concentrations of sucrose and ethanol-soluble fructan. Quantitative measurements of magnetization transfer (MT) indicated a smaller fraction of a solid or a restricted-mobility proton pool in the scales of the chilled bulbs. By contrast, the MT effect was significantly higher in the central bud of the chilled than in the nonchilled bulbs.
• Degradation of storage polysaccharides to low-molecular-weight sugar molecules during release from dormancy could be accompanied by local release of water molecules tightly bound to the polysaccharide granules into the bulk water, or by an influx of free water molecules due to increased osmotic potential caused by the raised sugar concentration, or by a combination of both effects.

Anil P. Ranwala

Papers

Sucrose-cleaving enzymes and carbohydrate pools in Lilium longiflorum floral organs

Analysis of nonstructural carbohydrates in storage organs of 30 ornamental geophytes by high-performance anion-exchange chromatography with pulsed amperometric detection.

Gibberellin4+7, Benzyladenine, and Supplemental Light Improve Postharvest Leaf and Flower Quality of Cold-stored `Stargazer' Hybrid Lilies

Preventive mechanisms of gibberellin4+7 and light on low-temperature-induced leaf senescence in Lilium cv. Stargazer

Water status and carbohydrate pools in tulip bulbs during dormancy release