Int. J. Curr. Res. Biosci. Plant Biol. 2015, 2(7): 101-108 International Journal of Current Research in Biosciences and Plant Biology ISSN: 2349-8080 Volume 2 Number 7 (July-2015) pp. 101-108 www.ijcrbp.com Original Research Article Succulence Leaf of Hoya Species Influence the Photosynthesis Type and Drought Avoidance Robika1, Triadiati2* and Sri Rahayu3 1Study Program of Plant Biology, Graduate School, Bogor Agricultural University, Dramaga Campus, Bogor 16680, Indonesia 2Department of Biology, Faculty of Mathematic and Natural Sciences, Bogor Agricultural University, Bogor 16680, West Java, Indonesia 3 Bogor Botanical Garden, Bogor 16003, West Java, Indonesia *Corresponding author. A b s t r a c t K e y w o r d s Hoya is an epiphytic plant which has succulent and non-succulent leaves. Succulence is known as one of the characteristics of Crassulacean Acid Metabolism (CAM) plant which is adapted to drought conditions. The aim of this study was to measure the Hoya’s photosynthesis pathway with different succulent leaves under drought condition. This study used five Hoya species i.e., H. verticillata and H. latifolia CAM cycling (succulent), H. bandaensis (semi-succulent), H. densifolia and H. multiflora (non- CAM Photosynthesis succulent). The results showed that the succulence of leaf affected Hoya’s photosynthetic pathway. Under well-watered condition, H. Verticillata, H. latifolia and Non-Succulent H. bandaensis showed pathway of CAM photosynthesis, while H. densifolia and H. multiflora showed intermediate activity of C3-CAM (CAM cycling). H. verticillata, H. Succulent Hoya species latifolia, and H. bandaensis were able to avoid from drought, which were characterized by no change in photosynthetic pathway during drought condition. On the contrary, H. densifolia and H. multiflora has a weak CAM photosynthesis due to the decrease of photosynthesis during drought condition. Introduction Anatomy of succulent Hoya leaf different with non- succulent Hoya leaves especially on the mesophyll Hoya is an epiphytic genus from Apocynaceae, thickness (Hafis et al., 2013; Hakim et al., 2013). subfamily Asclepiadoidea. There are about 150-200 Hoya species in the world (Burton, 1992) and 50-60 The main characteristic of succulence in the plant tissue species found in Indonesia (Rahayu, 2003). Distribution is their ability to store water to support their of Hoya started from the lowlands to uplands with physiological function when the external water is not common occurrence in lowlands (Rahayu, 2012). Hoya available (Ogburn and Edwards, 2012). Furthermore, the has morphology leaf thickness variations, from thick leaf succulent leaf tissue also have a role in storing and (succulent) to thin leaf (non-succulent) (Rahayu, 2010). accumulating organic acids required for physiological Robika et al. (2015) / Int. J. Curr. Res. Biosci. Plant Biol. 2015, 2(7): 101-108 101 Int. J. Curr. Res. Biosci. Plant Biol. 2015, 2(7): 101-108 function which perform a typical photosynthetic study by Hafis et al. (2013) and Hakim et al. (2013). pathway, namely Crassulacean Acid Metabolism (CAM) Plants material used stem cutting (2 nodes length). The (Kluge and Ting, 1978). selected plant material was collected from Bogor Botanical Garden collection. Two nodes of Hoya stem The advantages of plant with CAM metabolism has high cuttings were planted in sandy planting medium during water use efficiency (WUE), due to ability to avoid from one half month in the greenhouse condition. After one drought (Lüttge, 2004). Therefore, CAM is a key half month, stem cuttings were transferred to planting adaptation of photosynthetic carbon fixation to limited medium contained a tree fern log and cocopeat (5:1 water supply (Cushman and Borland 2002). The w/w). Stem cuttings were maintained for seven months characteristic adaptation of CAM plant to limited water before drought treatment. Measuring of growth rate was supply is nocturnal CO2 fixation and daytime CO2 re- conducted every week during 7 months. assimilation (Cushman and Borland, 2002; Lambers et al., 2008) and stomata closed during the day and opened Experimental design during the night (Taiz and Zeiger, 2010). One of criteria to determined CAM photosynthesis is presence daily The experiment was designed using a randomized block organic acid fluctuation (Cushman and Bohnert, 1999). design (RBD) factorial with two factors of treatment. The study has been done in many CAM species showed The first factor was five Hoya species. The second factor that highly succulence correlated with increased was drought treatment, namely: watered every 2 days nocturnal organic acid accumulation (Griffits et al., (control) and drought treatment for a period of 1 month. 2008). Several studied showed that Hoya had CAM Leaf succulence photosynthetic. Rayder and Ting (1983a) found that H. carnosa had CAM photosynthetic under well-watered, Leaf succulence was measured when the plant seven but it would shift from CAM to CAM-idling months old with parameters of succulence were: modification under water stress. The result of Lieth and Werger (1992) research showed that H. austrialis and H. Leaf thickness: it was measured with Micrometer. nicholsoniae indication strong CAM photosynthesis. Yusnaeni (2002) also showed that H. difersifolia, H. Saturated Water Content (Ogburn and Edwards, 2012): lacunosa, H. carnosa, H. macrophylla, and Hoya sp. had CAM activity (Full CAM) under sun habitat and watering every week. If they were grown in 75% shade with watering every day or every week, they had physiological adaptation, tend to C3 (CAM cycling). Relative Water Content (%) (Prochazkova, 2001): However, the previous studies on photosynthetic pathway did not correlated with the leaf succulence on the other species. Therefore, in this study we choosen five Hoya species with different leaf succulence i.e. H. verticillata, H. latifolia, H. bandaensis, H. densifolia, Succulence Mesophyll (Kluge and Ting, 1978): and H. multiflora under different watering to measure the Hoya photosynthetic pathway. Furthermore, five Hoya species would be analysed based on the leaf succulence correlate with its photosynthesis under drought condition. Organic acid content Materials and methods Measurements of organic acids in the leaves can be + determined by measuring the content of proton (H ) + Plant material and growth conditions (Medina et al. 1993). Measurement of H was done by using the acidity titration method following Griffiths et Plants material were chosen based on the data of leaf al. (2008) with modifications. Titratable acidity was anatomy with the different leaf succulence from previous conducted to analysed changes of leaf acidity during 20 h per day. Mature leaf disc (dia. 2 cm) from well watered Robika et al. (2015) / Int. J. Curr. Res. Biosci. Plant Biol. 2015, 2(7): 101-108 102 Int. J. Curr. Res. Biosci. Plant Biol. 2015, 2(7): 101-108 and drought were boiled in 4 ml aquadest for 20 min. (non succulent) (Table 1). These results are well Furthermore, the extract was cooled and titrated to pH 7 supported by previous studies on succulent Hoya species with 10 mM NaOH (Griffiths et al., 2008). with the changes observed in morphology (Rahayu, 2003) and anatomy (Hafis, et al., 2013; Hakim et al., Physiological parameters 2013). The increasing thickness leaves followed by an increase of SWC and RWC in succulent Hoya and semi Observation of physiological parameters was consisted succulent. H. verticillata had SWC and RWC of photosynthesis rate, transpiration rate, stomatal significantly different (p<0.05) with H. bandaensis, H. conductance, and Chlorophyll content measured by Licor densifolia and H. multiflora. H. bandaensis had leaf 6400 Xt Nebraska USA. Chlorophyll content was thickness lower than H. verticillata and H. latifolia, but analysed by using the method of Arnon (1949). higher than H. densifolia and H. multiflora. Therefore, H. bandaensis had Sm higher (p<0.05) than the other four Data analysis Hoya species (Table 1). Data was analysed by analysis of variance (ANOVA) Differences succulence leaf Hoya was due to differences and continued by DMRT/Duncan Test. in the anatomical structure of leaf. Hafis (2013) and Hakim (2013) reported that thickness of leaf, mesophyll, Results and discussion epidermis, and cuticle of succulent Hoya were thicker than Non succulent Hoya. The increasing of leaf Succulence of leaf Hoya species characteristics thickness correlated with increasing of mesophyll cells of leaf and then followed by an increasing SWC (Nelson Leaves of H. verticillata and H. latifolia (succulent) had and Sage, 2008; Ogburn and Edwards, 2012). Saturated thick leaves, higher Saturated Water Content (SWC), water content showed the water storage capacity in Relative Water Content (RWC) and Succulence mesophyll. SWC of succulent Hoya was higher than non Mesophyll (Sm) than H. densifolia and H. multiflora succulent Hoya. Table 1. Leaf thickness, Saturated Water Content (SWC), Relative Water Content (RWC), and Succulence mesophyll (Sm) of five Hoya species. Sm Leaf thickness SWC Species Leaf type RWC (%) (gH O/mg (µm) (gH O/g dry mass) 2 2 Chlorophyll) H. verticillata Succulent* 1220.56a 18.71a 95.29a 13.40b H. latifolia Succulent* 866.11b 17.16a 95.85a 7.83bc H. bandaensis Semi succulent 626.67c 13.98b 89.73b 23.17a H. densifolia Non succulent** 315.70d 8.91c 89.70b 3.43c H. multiflora Non succulent** 225.69d 6.40d 86.95b 1.01c Data in the table represent means. Different letter in the same column represent significantly difference at p<0.05 (Duncan’s test). Source comparison: (*) Rahayu (2010) and Hafis et al. (2013). (**) Rahayu (2010) and Hakim et al. (2013). Sm in five Hoya species were significantly different and Organic acid content influenced by leaf succulence with the range of Sm between 1.01 until 23.17 gH2O/mg chlorophyll. The Sm Organic acid content in Hoya leaf was measured by value indicated the level of leaf tissue succulence using H+ content in leaf tissue. The result showed that (Herrera et al., 2010; Deshmukh and Murumkar, 2013). two succulent Hoya species (H. verticillata and H.