A recent study of our group has shown that sugarcane plants previously exposed to cycles of water deficit and rehydration or those originated from material that faced water deficit had their photosynthetic performance and growth enhanced when exposed to a new drought event. Plant memory refers to the capacity of a previous exposure to stressful events triggers changes in gene expression patterns that regulate all plant development, allowing a more efficient and rapid response to recurrent stresses. This project aims to identify the molecular, metabolic and physiological markers that would be associated with memory to drought in sugarcane plants and to evaluate its inheritance and persistence in vegetatively propagated plants. For this purpose, untargeted large-scale metabolome and transcriptome analyses will be carried out on leaf, buds and root samples from plants exposed to cycles of drought and rehydration. We will also analyse the physiological and molecular responses of these plants, associating them with memory to drought and their inheritance in propagules. Based on the obtained data, we aim to propose new management practices for pre-sprouted sugarcane plants produced under nursery conditions. In addition, we aim to establish a platform for transcriptomic analysis in sugarcane, which will serve as a basis for the identification and understanding of the molecular mechanisms that allow memory inheritance to environmental stresses.

Funding: FAPESP (2019/06161-2); Period: Jun 2019 to May 2021; R$ 151.873,28

People: RV Ribeiro (PI); EC Machado; MD Pissolato; KA Vitti; SF Silva; AR Fernie; AP Domingos Jr; LP Souza; MW Ahchige

Biomass arises as an important clean energy alternative and fibrous plants fit well the requirements as raw material. Using the same productive system as sugarcane, energy cane is able to produce almost two times more dry matter per hectare than sugarcane varieties. This high biomass production of energy cane can be associated with its high tillering and a vigorous root system with the presence of rhizomes. These traits enable energy cane to capture more resources and, subsequently, convert more energy into biomass than sugarcane. The central objective of this work is to understand the physiological bases of biomass production by energy cane, giving special attention to the light interception and conversion efficiencies. A detailed study about photosynthetic traits of energy cane and sugarcane will be performed in potted plants under greenhouse conditions. Light and CO2 responses curves of photosynthesis performed under high (21%) and low (2%) O2 will allow us to access and estimate several in vivo variables related to the biochemistry, photochemistry and CO2 diffusion of energy cane and compare them to ones estimated in sugarcane. A field experiment will be carried out to estimate the light interception and conversion efficiencies, measuring light levels above and below canopy, plant growth and carbohydrate content throughout the crop cycle. As compared to sugarcane, we expect that the higher biomass production of energy cane is due to higher availability of photoassimilates based on higher light interception and conversion efficiencies. By knowing the physiological bases of biomass production, further improvement of biomass production by energy cane would be achieved through breeding.

Funding: CAPES (001)

People: LP Cruz (co-PI); VS Pacheco; RL Almedia; LM Silva; EC Machado; RV Ribeiro (PI)

The efficiency of photosynthesis and the integrity of the photosynthetic apparatus under fluctuating environmental conditions are important traits associated with crop yield. An alternative to increase crop yield is by developing cultivars with high sunlight conversion efficiency into biomass throughout the plant canopy, where leaves are exposed to different light intensities throughout the day. While top leaves are commonly exposed to direct sunlight, those ones at the bottom position receive less light as sunflecks, which account for 90% of all energy available for photosynthesis inside plant canopy. Such light dynamics require a sophisticated control mechanism for photosynthesis induction and deactivation of photoprotection mechanisms, increasing the efficiency of CO2 assimilation. We believe the fast induction of photosynthesis and fast relaxing of the non-photochemical quenching (NPQ) through plant canopy support high light conversion efficiency into biomass by plants and then high crop yield. Some variations in photosynthetic induction kinetics have been identified in soybean and wheat, but there are no integrative studies evaluating how photosynthesis induction and photoprotection varies through the canopy structure of C4 species such as sorghum, maize and sugarcane. The aim of this study is to investigate the genotypic variation of photosynthesis induction, NPQ relaxation, light distribution and canopy structure in genotypes of maize, sorghum and sugarcane.

Funding: FAPESP (2019/27106-0) and CAPES (001)

People: RL Almeida (co-PI); EC Machado; VS Pacheco; RV Ribeiro (PI)

A recent study developed by our group demonstrated that sugarcane plants previously exposed to cycles of water deficit and rehydration or originated from material that had undergone water deficit had their photosynthetic performance and growth favored when exposed to drought again. The previous exposure to stressful events can trigger changes in the pattern of gene expression that regulate all plant development and allow a more efficient and faster response in cases of recurrent stress, and this phenomenon is treated in the literature as plant memory. The aim of this proposal is to identify the molecular, metabolic and physiological markers that would be associated with memory and drought in sugarcane and to evaluate their inheritance and persistence in vegetatively propagated plants. For this purpose, a large-scale analysis of the main groups of primary metabolites and transcriptome will be performed on samples of leaves, stem buds and sugarcane roots exposed to drought and rehydration cycles. The physiological and molecular responses of these plants will also be analyzed by associating them with the drought memory and their seedlings inheritance. Based on the obtained data, its pretend to suggest new management practices for pre-broken sugarcane seedlings in nursery condition, besides establishing a platform for transcriptomic analysis on that species, which will serve as a basis for the identification and understanding of molecular mechanisms that allow the inheritance of memory to environmental stresses in sugarcane.

Funding: FAPESP (2019/27106-0) and CAPES (001)

People: MD Pissolato (co-PI); EC Machado; SF Silva; RV Ribeiro (PI)

The indoor cultivation is a concept based on growing plants in a closed system with artificial light and controlled temperature and water supply. With the improvement of technologies, the domestic vegetable production serves consumers looking for fresh and safer products, with better nutritional quality. In general, light intensity is low in indoor systems, and there is a need to establish light regimes that optimize vegetable production. Photoperiod is an environmental factor that plays an important \role in plant productivity and quality, being an external stimulus that controls the circadian cycle of plants. While some studies show that long photoperiods result in greater accumulation of biomass, others report the damages caused by the absence of dark. An essential point is that indoor production systems depend on cost-benefit, being necessary to evaluate the biomass produced per energy unit used. One would expected that under long photoperiods or under the absence of dark (photoperiod of 24 h), photosynthesis will decrease due to the circadian cycle, being offered light energy that is not used efficiently by plants. Here, we aim to evaluate how the photoperiod affects the ratio between leaf CO2 assimilation and light energy availability, also considering the accumulation of biomass and quality of lettuce plants. Lettuce plants will be germinated and conducted in floating hydroponics under varying photoperiod (12, 14, 16, 18, 20, 22 and 24 hours), maintaining the other environmental conditions constant. After 15 days of planting, leaf gas exchange will be monitored continuously for 48 h in each light regime. At the end of the crop cycle, the fresh and dry mass of the plants will be measured, as well as leaf area and number of leaves, as well as the contents of chlorophyll carbohydrates, nitrogen and nitrite. The energy used in each treatment will be measured to obtain the biomass produced per unit of energy and thus we will be able to compare the energetic efficiency of the indoor cultivation system in each photoperiod.

Funding: CAPES (001)

People: LM Silva (co-PI); LP Cruz; EC Machado; LF Purquerio; A Calori; RV Ribeiro (PI)

The practice of grafting affects the plant susceptibility to water deficit since rootstock and canopy exhibit different resistance to drought. In xylem vessels, the tension generated by transpiration can cause formation of embolism, which reduces the ability of plants to carry water. The vulnerability of branches to embolism varies throughout the growing season of plants as well as after a drought event. This study aims to evaluate the water relations of citrus species under field conditions and to reveal the structural and functional bases of embolims susceptibility, as well as to evaluate the association of these characteristics with the tolerance to drought in citrus. As hypotheses, we have that species and varieties of canopies grafted on the same rootstock present different hydraulic characteristics; rootstock species changes the susceptibility to embolism of canopies; hydraulic conductivity and vulnerability to embolism vary throughout the year, and the branches of trees with growing fruits have higher hydraulic conductivity. For this, we will do a study of hydraulic characterization of different canopy/rootstock combinations with importance for Brazil, besides a study of the seasonal variation of these characteristics in plants in the field. The hydraulic conductivity, hydraulic safety margin, anatomy, contribution of aquaporins to water transport, water potential and leaf gas exchange in orange trees of the Valencia, Pêra and Hamlin varieties, of Ponkan mandarin and of Tahiti lime based on Rangpur lime and Valencia sweet orange grafted on Rangpur lime, citrumelo Swingle and citrandarin. The selection of drought tolerant materials could be anticipated by understanding the characteristics that induce greater embolism resistance, this may be a tool used in citrus breeding programs.

Funding: FAPESP (2018/09834-5); Period: Jan 2019 to Dec 2021; R$ 163,229.04

People: MT Miranda; L Pereira; EC Machado; RV Ribeiro (PI)

The soil water deficit is the cause of negative pressure in the xylem, which can result in an abrupt change of the water meta-stable state, forming bubbles and interrupting water transport. Although embolism is well-known to occur, the xylem hydraulic properties that allow the transport of water under negative pressure and the physico-chemical properties that prevent constant embolism formation are poorly understood. One of these properties is the wettability of the xylem wall, which can nucleate or stabilize bubbles. Also, mechanisms that allow the control of hydraulic conductance under negative pressure are not completely known due to the limitations of existing methods. In fact, studies on water transport and embolism are hampered not only by the micro and nanometric scale structures involved but also several embolism artifacts due to handling a sample with water under negative pressure. Thus, in order to better understand the mechanisms that regulate water transport and enable resistance to embolism, new methods are required to minimize or even circumvent possible artifacts and to provide reliable data. We propose here the development of three different methods that will allow us (a) to estimate embolism in vivo, based on the pneumatic method originally developed for measurements of cut branches, (b) to estimate the xylem wettability based on a new hydraulic apparatus described in this project, and (c) to evaluate key factors determining the xylem hydraulic conductance, such as radial conductance and aquaporins. Based on these new methods and approaches, we will reveal the hydraulic properties of orange, coffee and eucalyptus trees, seeking a better understanding of drought resistance in these economic species.

Funding: FAPESP (2017/14075-3); Period: Mar 2018 to Jul 2021; R$ 299,773.26

People: L Pereira (PI); S Jansen; RV Ribeiro)