Mixotrophic in vitro cultivations: the way to go astray in plant physiology

Abstract

Rate of photosynthesis and related plant carbohydrate status are crucial factors affecting plant vigor. Sugars providing carbon and energy sources serve also as important signaling molecules governing plant growth and development through a complex regulatory network. These facts are often neglected when mixotrophic cultivation of plants in vitro is used, where artificial exogenous sugar supply hinders studies of metabolism as well as sugar‐driven developmental processes. We compared the growth, selected gas‐exchange parameters and sugar metabolism characteristics in four model plants, potato (Solanum tuberosum ‘Lada’), tobacco (Nicotiana tabacum ‘Samsun’), rapeseed (Brassica napus ‘Asgard’) and strawberry (Fragaria vesca), under both photomixotrophic (PM) and photoautotrophic (PA) conditions. To ensure PA conditions, we used our improved sun caps that serve as gas and light permeable covers for cultivation vessels. We found bigger biomass accumulation, larger leaf areas, higher stomatal conductance and higher instantaneous water use efficiency and lower root sugar contents in PA plants compared to PM ones. However, for other characteristics (root biomass, root/shoot ratio, pigment contents, leaf sugar and starch levels and transpiration rates), a strong species‐dependent reactions to the exogenous sugar supply was noted, which does not allow to create a general view on the overall impact of PM nutrition under in vitro conditions.

The Effect of Sucrose Supplementation on the Micropropagation of Salix viminalis L. Shoots in Semisolid Medium and Temporary Immersion Bioreactors

“…In papaya, using a stationary liquid culture with zeolite supported more rooting and the survival of shoots cultured without sugar and exposed to high ventilation was reported [55]. Within plants cultured in SSM results seem to be more variable: grapevine and kiwi fruit shoots cultured in SSM rooted and acclimatized better with sucrose [56,57], in rapeseed no correlation could be established [45], whereas with thyme, paulownia, potato, tobacco and wasabi more roots were formed when less sugar was added to the culture medium [29,33,45,58]. In strawberry, contradictory reports have been reported, as Ševčíková et al [45] did not observe an increase in the root mass when sugar was not added to the medium, whereas Nguyen et al [29] reported more and longer roots in photoautotrophic conditions.…”

“…Lack of correlation between photosynthetic pigments and growth has been reported for other plants such as myrtle [43], chestnut [44], apple [28], tobacco, potato, strawberry, and rapeseed [45] and V. condensata [32]. Even if chlorophylls and carotenoids drive photosynthesis by absorbing energy from light, photosynthesis is dependent on other major physiological and biochemical processes including CO 2 stomatal and mesophyll conductance and the biochemistry driven by the Rubisco enzyme system [46,47].…”

“…Regarding micropropagated plants, some of the key factors influencing photosynthesis have been studied in shoots cultured with or without exogenous sugar supplementation [49][50][51]. It has been reported that Rubisco decreased in avocado micropropagated with high sucrose content even when grown with CO 2 -enriched air [52], but it seems that the concentration of this enzyme in micropropagated plants is species-dependent [53], as reported for other biochemical parameters [45]. In our case, all the treatments with high proliferation exhibited high pigment content, but we cannot attribute the improvement in the yield of willow shoots cultured in TIS without sugar specifically to a superior content in photosynthetic pigments.…”

Case Study of Effects of Mineral N Fertilization Amounts on Water Productivity in Rainfed Winter Rapeseed Cultivation on a Sandy Soil in Brandenburg (Germany) over Three Years

“…Broad bed and furrow and raised bed land configurations along with residue and hedge leaves mulching under no-till improved soil quality and was the most suitable for higher returns of groundnut-rapeseed system under rainfed condition. Crop rotation: The work of [47] investigated mixotrophic cultivations and found higher instantaneous water use efficiency in photoautotrophic conditions compared to photomixotrophic rapeseed plants. Breeding: The work of [48] investigated two contrasting rapeseed genotypes, Qinyou 8, drought-sensitive, and Q2, drought-tolerant.…”

Effect of Sucrose on Growth and Stress Status of Castanea sativa x C. crenata Shoots Cultured in Liquid Medium

“…High sucrose concentrations may cause hyperhydricity and other disorders [ 29 ]. It has been claimed that the elimination of sugar from micropropagation nutritive media promotes photosynthetic activity, producing a healthier physiological state and increasing the speed of plantlet adaptation to greenhouse conditions [ 30 ].…”