# Plant Growth Regulators Improve the Production of Volatile Organic Compounds in Two Rose Varieties
## 1 Introduction  
Most floral scents are considered pleasant; they have played key roles in the early development of flowers [1]. The genus _Rosa_ is comprised of between 100 and 200 species and more than 18,000-24,000 commercial cultivars most of which are hybrids; collectively, these are based on only eight wild species [2; 3; 4]. Hybrid tea and Floribunda roses are considered modern roses and are popular in Australia [5]. The main commercial and industrial uses of roses are based on the perfume and floriculture industries, the former of which relies on scented rose varieties [6]. There are many studies on the emission of rose volatiles but few discuss modern rose varieties [7]. Many factors affect the emission of aromatic compounds, among which are plant growth regulators (PGRs) [8]. Plant growth regulators (PGRs) are produced naturally by plants or synthetically by chemists and play a key role in life cycles of plants [9]. PGRs include cytokins and auxins, which are small molecular compounds that at low concentrations regulate plant developmental processes [10]. Benzyladenine (BA) and naphthalene acetic acid (NAA) have both been applied pre- and post-harvest to many ornamental plant species. Cytokins such as BA are used to improve the quality and vase life of cut flowers. Moreover, BA promotes cell elongation and division, decreases flower drop and increases flower production [11]. BA has also been used to improve the growth and development of aromatic plants. Treating _Lantana camara_ L. plants with BA at 0.44 and 4.4 \(\upmu\)mol/L increased volatile organic compound (VOC) production, which was detected by solid phase micro-extraction (SPME) [12]. Similarly, [PERSON] et al. [13] indicated that the production of VOCs increased with the application of different PGRs, such as 0.57 \(\upmu\)M indole-3-acetic acid (IAA), 0.45 \(\upmu\)M thidiazuron, 9.3 \(\upmu\)M kinetin and 4.4 \(\upmu\)M BA, when applied to _Agastache rugosa_ (Fisch. Et C. [PERSON]) plants grown in vitro. Another study on _Stevia rebaudiana_ L. plants reported that BA and IAA added to tissue culture media significantly influenced the in vitro production and distribution of secondary metabolites to produce strong antioxidant activity [14]. Auxins such as NAA coordinate many growth and behavioral processes in plant life cycles. Furthermore, NAA induces cell division and elongation, plays a key role in shoot development, and increases flower production [10]. A study on _Rosa damascena_ (Damask rose) indicated that the application of NAA at 25 mg/L to rose plants, increased flower longevity, plant height, flower yield and flower oil content [15]. A study by [PERSON] and [PERSON] [16] showed that the addition of 0.1 mg/L NAA and 1 mg/L BA to a cell suspension culture of _Digitalis lanata_ (Grecian foxglove) increased the production of flavonoids, which are related to secondary metabolite production. Another study, by [PERSON] et al. [17], indicated that the addition of BA (0.2 mg/L), kinetin (0.1 mg/L) and NAA (0.05 mg/L) together with a mineral salt (MS) medium enhanced the production of secondary metabolites in the shoot cultures of _Hypericum hirsutum_ and _H. macultatum_ plants. Little information is known about the influence of these PGRs on secondary metabolite production [18]. To our knowledge, there has been no research reported to date on the influence of NAA on volatile production in rose plants. The detection of VOCs is widely used by scientists because of their wide range of beneficial pharmacological and biological activities [19]. Currently, more than 400 VOCs have been identified from rose flowers [20]. The headspace solid phase micro-extraction (HS-SPME) is a method for the extraction of VOCs from plants; it is now commonly used [21]. HS-SPME is a pre-concentration technology, which integrates extraction, concentration and sampling, and is a simple, fast and solvent-free preparation method for the extraction of VOCs [22]. It also prevents the production of artifacts compared with conventional solvent extraction procedures [23].