Progesterone and androstenedione involved in plant growth.
Sex hormones are steroid hormones that interact with vertebrate androgen or estrogen receptors. They have been found as messengers to promote the maturation of sexual organs, the development of secondary sex characteristics, regulation on pain perception and maintain sexual function (Bińkowska, & Woroń, 2015). Various forms of estrogen derivatives have been widely used in contraception, treatment of menopausal syndrome in women, prostatic hypertrophy in men and other endocrine disorders (Maurer, Lissounov, Knezevic, Candido, & Knezevic, 2016).
Progesterone (PROG) is one kind of mammalian gonadal hormone necessary for the regulation of ovulation and menstruation. It is now detected in a range of plant species (Tarkowská, 2019). It was reported that the PROG contained in some plant tissues even exceeded 2600 ng/g (dry weight) (Iino et al., 2007). Five secondary steroids as the mammalian gestagen PROG are found in Adonis aleppica and Juglans regia (Tarkowská, 2019; Pauli, Friesen, Gödecke, Farnsworth, & Glodny, 2010). They assume a variety of physiological functions in plants. For instance, the Arabidopsis seedlings were found to be promoted by PROG at low concentrations but suppressed at higher concentrations (Iino et al., 2007). A similar phenomenon is found in sunflowers. High PROG concentration (0.25 μg per plant) stimulated the elongation of shoots, while a lower concentration (0.1 μg per plant) stimulated the growth of sunflower roots (Bhattacharya, & Gupta, 1981). In addition, PROG can regulate plant mineral management, including calcium, magnesium, phosphorus, sulfur, copper and so on (Dumlupinar, Genisel, Erdal, Korkut, & Taspinar, 2011). Furthermore, it was reported that PROG (1 and 10 μM) induces the flowering in winter wheat. Same as androstenedione (0.1 μM) in Arabidopsis thaliana which leads to more than twice as generative percentage compared to control (Janeczko, Filek, Biesaga-Kościelniak, Marcińska, & Janeczko, 2003). In terms of environmental resistance, PROG alone (0.1 µmol L−1) can alleviate cold stress by modulation of mitochondrial respiratory pathway (Erdal, & Genisel, 2016). Potential role of PROG in response to oxidative damage (10−6 M) is demonstrated by influence oxidative enzymes such as SOD, POX and CAT (Erdal, & Dumlupinar, 2011).
The androstenedione (AN) is another common sex hormone precursor in both sexes and takes charge of the biosynthesis of testosterone (Haring et al., 2012). New result demonstrated the effect of androstenedione (1 µM) on winter wheat exposed to low temperature (Janeczko et al., 2018). A key role for AN is to mitigate damages caused by freezing temperatures and enhance frost resistance in wheat. Moreover, there has been found an interaction between animal hormone and plant hormone in wheat. AN triggers an accelerated generative development of wheat via increasing GA3 and cytokinins (Janeczko et al., 2018). The frost resistance increases in the process due to AN-induced changes in redox homeostasis. In addition, AN regulates enzyme activity including superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), polyphenol oxidase (PPO) and alpha-amylase against oxidative damage in endosperm of maize seeds (Erdal, 2012). Androstenedione can alleviate drought stress and compensate efficiency of photosystem II in soybean by possible effect on aquaporin functionality and membrane stability (Janeczko, Kocurek, & Marcińska, 2012). These studies provide new insights into AN as a novel plant growth regulator to improve resistance in crop.
Furthermore, the ability of plants to convert sterols into steroid hormones is found, involving progesterone, testosterone, androstadienedione, androstenedione, and estrogens. This means that plants have endogenous steroid hormones just like animals. However, the biological activity of these hormones remains to be explored (Tarkowská, 2019).
Oxytocin affects the production of secondary plant constituent in vitro
Oxytocin is a neuropeptide widely used by medical doctors and veterinarians (Perry, 2014). Previous review demonstrated its role in the dynamic function of the social brain, such as result in changes in brain activity and delivery in pregnant mammals (Perry, 2014; Gordon et al., 2013). The oxytocin signaling system is ubiquitous across the animal kingdom.
Oxytocin affects the production of secondary plant constituent in vitro. The influence of oxytocin (100 μg/L) on biomass accumulation as well as on the production of glycyrrhizin, a key phytoconstituent of liquorice used in the pharmaceutical and food industries (Yu et al., 2017), was observed in the cell cultures of Abrusprecatorius (Karwasara, Tomar, & Dixit, 2011). Moreover, the article demonstrated the use of oxytocin to increase the growth of pumpkins and cucumbers in India (None, 2009). However, information about the function and regulation of oxytocin in planta is still limited. These would be worthwhile avenues to explore.