Hyperhydricity in turbinicarpus cultures. Shoot development under the influence of the medium

Symptoms and scope of the phenomenon

Hyperhydricity is a developmental disorder in plant cultures accompanied by excessive hydration and altered tissue structure. Cactus shoots develop translucency, glossiness and brittleness. High humidity and direct contact with the medium create conditions favouring this state. In the described experiment with Turbinicarpus valdezianus, symptoms were assessed from shoot appearance. [García Osuna et al. 2011, pp. 176–177]

Parenchyma in a healthy cactus stores water as part of normal stem organisation. Hyperhydricity involves both abnormal shoot form and anatomical changes. In the study, preparations of symptomatic plants had enlarged cells and altered vascular tissues. Material quality can therefore be assessed through morphology and anatomy alongside the volume of growth obtained. [García Osuna et al. 2011, pp. 176–178, Fig. 1]

Experimental conditions

García Osuna and colleagues' experiment was conducted in 2006, and the results published in 2011. The starting material consisted of healthy T. valdezianus shoots about 0,5 cm in diameter and 0,8 cm high, cut transversely into fragments. The MS medium contained 30 g/L sucrose, 8 g/L agar and 1 mg/L kinetin. Its pH was 5,7. The control and treatments with the tested additives received the same basal medium. [García Osuna et al. 2011, pp. 176–177]

Cultures were maintained in glass vessels of 60 mL capacity containing 20 mL of medium at 25 ± 1°C. Lighting lasted 16 hours at 2500 lux, followed by eight hours of darkness. Medium was replaced every four weeks. Each treatment had five replicates of four explants, fragments of the plant placed in culture. The experiment was performed three times and mean results presented. [García Osuna et al. 2011, p. 177]

Paclobutrazol was tested at 3,4 × 10⁻⁴ M, and prohexadione-calcium, salicylic acid and benzoic acid each at 10⁻⁴ M. All shoots were therefore exposed to kinetin, while the added compound created the difference between treatments. Describing the control as lacking an additional test compound precisely reflects this experimental design. [García Osuna et al. 2011, p. 177, Table 1]

Multiplication and symptom frequency

Letters beside shoot numbers denote groups differing in Tukey's test at a threshold of p < 0,05. The paclobutrazol treatment had significantly more shoots than the others. The value 0% means that no explants with recognised symptoms were observed in this culture. Percentages describe the frequency of morphologically assessed symptoms. The study did not measure percentage water content in the shoot. [García Osuna et al. 2011, pp. 177–178, Table 1]

Prohexadione-calcium, salicylic acid and benzoic acid increased symptom frequency relative to the control. The direction of the particular culture's response arose from the compound, dose and remaining medium composition. The paclobutrazol effect concerns the T. valdezianus material used and the observation period. Increased shoot numbers and normal appearance are separate results that occurred together in this treatment. [García Osuna et al. 2011, pp. 177–178]

A growth regulator and a change in habit

Paclobutrazol restricts synthesis of gibberellins, hormones involved in processes including cell elongation. The authors relate the culture's response to its interaction with kinetin. The experiment compared development and anatomy without directly measuring hormone concentrations. The relationship between the regulator's known action and the observed response is a biological explanation proposed in the paper. [García Osuna et al. 2011, pp. 176–177]

Conditions favouring formation of numerous shoots also changed rooting. In the paclobutrazol treatment, root number was lower and root length greater than in the control. Salicylic acid also influenced root length despite frequent hyperhydricity symptoms. Choosing a culture treatment therefore requires assessment of several traits of the material obtained, which can respond in different directions. [García Osuna et al. 2011, pp. 177–178, Table 1]

What shoot sections reveal

Sections of symptomatic material had larger, more varied cells. Xylem vessel traits also changed. The study included representative material from individual treatments, examined after fixation and staining. Anatomy complemented assessment of shoot appearance by showing internal changes accompanying hyperhydricity. [García Osuna et al. 2011, pp. 177–178, Fig. 1, Table 2]

The authors discuss a possible contribution of oxidative stress to the response to salicylic acid and benzoic acid. However, they did not measure reactive oxygen species or antioxidant defence enzyme activity in this experiment. This is a proposed mechanism based on observations and earlier literature. Their own data cover growth response, symptoms and the structure of preparations. [García Osuna et al. 2011, pp. 176–178]

A second research system, a hybrid culture

For Turbinicarpus × mombergeri, a hybrid of T. laui × T. pseudopectinatus, the abstract of a 2022 paper describes reduced hyperhydricity through changes in mineral concentrations, an increased calcium proportion and use of polyethylene glycol. The authors subsequently obtained rooted plants transferred to substrate. This involves different material and a different medium system from the T. valdezianus experiment. [Santos-Díaz et al. 2022, abstract]

POWO accepts Turbinicarpus × mombergeri [2-WWW] as a hybrid. The original publication title uses the spelling ‘Turbincarpus mombergeri’, retained in the reference list. The atlas text uses the accepted name with an indication of hybrid origin. [2-WWW]

From a shoot to a plant outside culture

Multiplication, rooting and acclimatisation form successive regeneration stages. A normal-looking shoot may have different root numbers and lengths from material produced in another medium treatment. The T. valdezianus experiment demonstrates this independence. A full quality description requires linking shoot traits with rooting and then with actual survival after transfer out of culture. [García Osuna et al. 2011, pp. 177–179]

The 2011 paper contains conclusions about the importance of rooting for acclimatisation but does not present a separate table of long-term survival outside culture. Its quantitative results mainly describe the state of the material in the in vitro experiment. Distinguishing these stages retains the proper data scope and allows multiplication rate and subsequent plant development to be compared separately. [García Osuna et al. 2011, pp. 178–179]