Seed hydration memory in Sonoran Desert cacti and its ecological implication

Abstract

Cactus seeds on the soil surface in the desert are subjected to periods of drought that last for up to a few months, and thus they are typically under discontinuous hydration (or discontinuous dehydration). Apparently, they can tolerate long periods of dehydration after single or multiple hydration events and subsequently germinate in accordance with the previous hydration experience. This was verified in three cactus species from the Sonoran Desert. Seeds of Stenocereus thurberi hydrated for 72 or 80 h followed by a dehydration period lasting for 4, 14, 70, 120 or 181 d germinated 2–3 d earlier and had 1.4–2 times shorter mean germination time (MGT) than untreated seeds. Seeds given shorter hydration periods also began to germinate sooner than the controls. MGT was shorter only when the hydration period was 48 h or longer. Final germination percentages were not affected by these treatments, only the MGT. Except for differences in germination percentages, similar results were found for Pachycereus pecten‐aboriginum and Ferocactus peninsulae. When the cycle of 24 h hydration followed by 4 d dehydration was repeated one or two times, the effect was cumulative: MGT was equal to 48 and 72 h hydration, respectively. These results suggest a phenomenon of “seed hydration memory,” the ability of seeds to retain during dehydration periods those physiological changes that result from seed hydration. Thus, treated seeds subsequently germinated earlier then untreated seeds, regardless of the duration of dehydration period. This led to a greater biomass accumulation and thus to higher survival in seedlings from treated than from untreated seeds.

Differential RNA- and protein-expression profiles of cactus seeds capable of hydration memory

“…The MGT was thus significantly reduced after HD treatment (P , 0.05 Student's t-test, Fig. 1B) as previously observed in this species (Dubrovsky, 1996). Based on these data, we concluded that in the present work we had successfully reproduced the hydration memory phenomenon.…”

“…Previously, we have successfully reproduced this phenomenon by germinating F. peninsulae seeds; we observed that the germination time was dramatically reduced after an HD cycle, as expected (Dubrovsky, 1996(Dubrovsky, , 1998. As an initial approach to describing the molecular events that lead up to the enhanced germination after an HD cycle, we aimed to investigate whether there was differential expression of total proteins of seeds and seedlings subjected to the HD cycle.…”

Effect of environmental heterogeneity on field germination of Opuntia tomentosa (Cactaceae, Opuntioideae) seeds

“…The erratic precipitation at the beginning of the rainy season in 1999, the consequent damping and drying of soil and the time over which the seeds were exposed to such fluctuations, as well as variations in temperatures, could weaken the funicular envelope, favoring germination in the control seeds of O. tomentosa by forming a germination valve and a water channel and/or invigorating the embryo (loss of physiological dormancy, Orozco-Segovia et al, 2007). On the other hand, it has been demonstrated that permeable seeds of columnar cacti have a hydration memory that improves germination after seeds are exposed to hydration-dehydrationrehydration treatments (Dubrovsky, 1996(Dubrovsky, , 1998; when such Fig. 4.…”

Effects of seed hydration memory on initial growth under water deficit of cactus from two populations that occur in different ecosystems in Northeast Brazil

“…HD cycles play an important role in the persistence and dynamics of plants in these ecosystems (Wilson & Witkowski 1998;Lima & Meiado 2017). Dubrovsky (1996Dubrovsky ( , 1998 points out that discontinuous hydration gives the seeds a high survival rate during desiccation, demonstrating that these seeds may present seed hydration memory, which preserves the characteristics resulting from previous hydration. A significant increase in germinability and germination speed and acquisition of higher tolerance of abiotic stresses are also results of HD cycles (Dubrovsky 1996;Rito et al 2009;Lima & Meiado 2017).…”