The Role of Abscisic Acid in Induction of Androgenesis: A Comparative Study Between Hordeum vulgare L. Cvs. Igri and Digger

Abstract

Under the same mannitol pretreatment and culture conditions, regeneration efficiency in the barley cultivar (cv.) Igri was about 10 times higher than in the cv. Digger, a difference only partially reflected by a difference in viable microspores after anther pretreatment. Therefore, a comparative study between cvs. Igri and Digger was carried out under various pretreatment conditions. For both cultivars, under water, CPW buffer and mannitol pretreatment conditions, there was a positive correlation between microspore viability and regeneration efficiency in that mannitol > CPW buffer >> water. Mannitol pretreatment of cv. Igri produced a much higher endogenous abscisic acid (ABA) level than as to Digger. Addition of ABA stimulated both percentages of viability and regeneration efficiency except in the case of mannitol pretreatment. Under CPW buffer pretreatment conditions, addition of ABA significantly stimulated regeneration efficiency and was ABA concentration dependent. However, cv. Digger was less responsive to ABA than cv. Igri. In both cultivars, under less optimal pretreatment conditions (e.g., water and CPW buffer), the effect of ABA was to stimulate increased percentages of viability and/or to reduce the number of binucleate microspores. Moreover, in cv. Igri, direct culture of anthers for 4 days without pretreatment caused an increased number of binucleate microspores compared with microspores with pretreatment for 4 days. These binucleate microspores showed DNA degradation in the nuclei. However, with mannitol pretreatment binucleate microspores and DNA fragmentation in the nuclei of microspores was rarely observed. On the basis of our observations, we suggest that the difference in regeneration efficiency in cv. Igri and cv. Digger is related to the differences in endogenous ABA production levels under mannitol pretreatment and responsiveness to ABA. One of the effects of ABA is likely due to an inhibition of cell death.

Stress-induced changes important for effective androgenic induction in isolated microspore culture of triticale (×Triticosecale Wittm.)

“…In this respect, our data confirm results obtained previously by other authors (Imamura and Harada 1980;Davies and Jones 1991;Van Bergen et al 1999;Wang et al 2000). The ABA effect was much stronger in anthers of 'Mieszko', for which low temperature pretreatment was essential to increase microspores viability and enabled induction of androgenesis.…”

“…Davies and Jones (1991) also reported production of ABA in response to treatment with high osmoticum and low temperature. It was also confirmed in studies of Van Bergen et al (1999) in barley anther cultures. Wang et al (2000) suggested that ABA and its signal transduction pathways may be considered as signaling factors involved in the reprogramming of microspore development.…”

“…According to Gorbunova and Kruglova (1996) ability to androgenic induction is controlled by endogenous growth regulators, especially the ABA level. Imamura and Harada (1980) and Van Bergen et al (1999) suggest that specific threshold level of ABA is required for the change of microspore developmental pathway. In studies of Wang et al (1999), the content of ABA in anthers of barley treated with starvation and osmotic stress increased almost twice and it was positively correlated with the microspore viability.…”

Androgenesis-inducing stress treatments change phytohormone levels in anthers of three legume species (Fabaceae)

“…Cold pre-treatment was similarly found to be beneficial for barley (Hordeum vulgare L.), tobacco (Nicotiana tabacum L), or triticale (9Triticose-cale) androgenesis due to improved microspore viability and increased response (Imamura and Harada 1980;van Bergen et al 1999;Wang et al 1999;_ Zur et al 2008). However, pyramiding other stresses such as centrifugation or electroporation on top of the cold stress did not increase ABA levels, indicating no additive effect of the different treatments.…”

Androgenesis Revisited

“…Although little is known in this respect, abscisic acid (Maraschin et al, 2005(Maraschin et al, , 2006Reynolds & Crawford, 1996;Tsuwamoto et al, 2007;van Bergen et al, 1999) and some plant extracellular signal-regulated kinase homologues (Coronado et al, 2002;Seguí-Simarro et al, 2005) have been proposed as intermediate transducers of extracellular stress signals for the activation of specific gene expression programs (reviewed in Seguí-Simarro & Nuez, 2008a). Related to the cellular response to stress, changes in the levels of different heat-shock proteins (HSPs) have been described in several species during stress-induced microspore embryogenesis after exposure to heat, colchicine, or starvation stress (Cordewener et al, 1995;Seguí-Simarro et al, 2003;Smykal, 2000;Zarsky et al, 1995).…”