text: Moreso than other enzymes in the Calvin cycle, SBPase levels have a significant impact on plant growth, photosynthetic ability, and response to environmental stresses. Small decreases in SBPase activity result in decreased photosynthetic carbon fixation and reduced plant biomass. Specifically, decreased SBPase levels result in stunted plant organ growth and development compared to wild-type plants, and starch levels decrease linearly with decreases in SBPase activity, suggesting that SBPase activity is a limiting factor to carbon assimilation. This sensitivity of plants to decreased SBPase activity is significant, as SBPase itself is sensitive to oxidative damage and inactivation from environmental stresses. SBPase contains several catalytically relevant cysteine residues that are vulnerable to irreversible oxidative carbonylation by reactive oxygen species (ROS), particularly from hydroxyl radicals created during the production of hydrogen peroxide. Carbonylation results in SBPase enzyme inactivation and subsequent growth retardation due to inhibition of carbon assimilation. Oxidative carbonylation of SBPase can be induced by environmental pressures such as chilling, which causes an imbalance in metabolic processes leading to increased production of reactive oxygen species, particularly hydrogen peroxide.  Notably, chilling inhibits SBPase and a related enzyme, fructose bisphosphatase, but does not affect other reductively activated Calvin cycle enzymes.
  The sensitivity of plants to synthetically reduced or inhibited SBPase levels provides an opportunity for crop engineering. There are significant indications that transgenic plants which overexpress SBPase may be useful in improving food production efficiency by producing crops that are more resilient to environmental stresses, as well as have earlier maturation and higher yield. Overexpression of SBPase in transgenic tomato plants provided resistance to chilling stress, with the transgenic plants maintaining higher SBPase activity, increased carbon dioxide fixation, reduced electrolyte leakage and increased carbohydrate accumulation relative to wild-type plants under the same chilling stress. It is also likely that transgenic plants would be more resilient to osmotic stress caused by drought or salinity, as the activation of SBPase is shown to be inhibited in chloroplasts exposed to hypertonic conditions, though this has not been directly tested. Overexpression of SBPase in transgenic tobacco plants resulted in enhanced photosynthetic efficiency and growth. Specifically, transgenic plants exhibited greater biomass and improved carbon dioxide fixation, as well as an increase in RuBisCO activity. The plants grew significantly faster and larger than wild-type plants, with increased sucrose and starch levels.